Vision is the one sense we humans rely on the most. We usually identify things by sight rather than sound or smell. It is for this reason that creators of visual media will make sure that things look different enough for the audience to easily recognize and tell apart. It can also be a form of visual shorthand for characterization, so that the audience can tell certain things about a character or setting without having to be told.
In addition, to the audience, this trope may be used in-Universe so that the characters can easily tell the difference between groups or things.
One way to do this is to use colour as an indicator that two things are different (when using different colours) or two things belong to the same category (when using the same colours). Colour can indicate who is the good guy and who is the bad guy, they can indicate personality type, they can say things about gameplay elements in a video game, which organization or group the person belongs to, and so on.
In Real Life colors are often used to distinguish everything from the meaning of lights, to wires, labels, faucets and other signs.
Bright, contrasting colors, particularly primary and complementary colors, are the most common. Regardless what they're used to symbolize, when things are color coded you can almost always count on a Red and a Blue. Further seeing a Green or a Yellow is also common. Purple and Orange are more rare unless you have enough units for a full Rainbow Motif or more.
Compare Good and Evil for Your Convenience, Sound-Coded for Your Convenience, Dress-Coded for Your Convenience.
Please only list examples that do not fall under one of the above subtropes.
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A Growing Affection has Shozokus, a certain ninja army who wear full stealth uniforms color coded by rank and approximate skill level (see the fic's main page for the full list).
In Clouded Sky, there are temples dedicated to each Pokémon type, and the acolytes of the temples dress in colors that correspond with the type their temple represents (Fire Temple = Red, Water Temple = Blue, etc.).
In the Gochuumon wa Usagi desu ka? manga, Chino mentioned the town requires that its buildings to show the occupations of the occupants by this trope. For example, fishmongers will need to paint their houses blue, and bakers pink.
In My Little Unicorn, Unicorns of a certain color tend to live in a specific area of Unicornicopia. For example, blue unicorns live in Bluesville. The only remotely clever name is O-Range for orange unicorns.
Disney's Aladdin has color motifs based on its desert setting. Blue (water) = good, red (heat) = evil, and yellow (sand) = neutral.
In the Brotherhood series of films, the hero always wears white boxers, while all the other villanous characters wear black underwear.
In Back to the Future, the DeLorean's LED displays are red for "Destination Time", green for "Present Time", and yellow for "Last Time Departed", in homage to to The Time Machine 1960. In Part III, Doc has made presto logs, color-coded green, yellow and red in increasing order of the amount of heat each produced to make their train run faster, with a corresponding gauge showing when it would happen.
The prisoners in Con Air: Normal inmates get Blue, the really scary ones get Orange, and the pants-wettingly scary Steve Buscemi gets White.
Epic: The rich greens and golds of the forest (the use of yellow contributing to the 'warmness'), versus the cold colour palette and mud-browns of Mandrake and his allies. Also, the brightness of the forest, compared to the relatively subdued colours used in the house.
In The Hunt for Red October, different color lighting was used for each submarine's interior to aid the viewer in quick recognition of which submarine it was and to minimize confusion.
In Kamen Rider X Super Sentai Superhero Taisen, Kamen Rider OOO will lend his medals to the Gokaigers, allowing them to transform into OOO's combo forms. With one exception, the general coloring of OOO's combos match up with the Gokaigers' colors (red, blue, yellow, green, and white [standing in for silver]), and they transform accordingly. The exception is Gokai Pink, who instead gets the purple combo.
In Logan's Run, the people who lived in the city wore clothes that matched their ages and the color of their life clocks. The sandmen, who were essentially portrayed as being evil, wore black and gray, even when they were in the gym or at home.
In the 1920 silent film The Mark of Zorro, Zorro instructs his allies to ride black horses on their night's mission to rescue some unjustly-jailed prisoners. The soldiers that pursue them conveniently all have light-colored horses, making it easy for viewers to keep track of which band of riders is which.
The Princess and the Frog: Dr. Facilier wears a black Baron Samedi-esque outfit while Mama Odie wears white, which is the traditional color for voodoo garb. This also fits with the way they represent shadow and light respectively. Purple, traditional hallmark of comic book villains, is part of the Doctor's costume and no one else, even though it's one of the standard Mardi Gras colors (Purple, Green and Gold). The person who wrote the color script made a conscious decision to include the three Mardi Gras colors: Facilier has purple in all of his scenes (since, of the three colors, purple is the most "unnatural"), the scenes in the swamp with frog Tiana and Naveen are green, and Mama Odie's scenes are awash in gold.
In Rebel Without a Cause, the color red is used often as a motif. For example, Judy's coat at the beginning of the movie, Jim's jacket, one of Plato's socks, etc.
In Star Wars, this tends to overlap with Good Colors, Evil Colors, such as the blue and green lightsabers of the Jedi vs. the red of the Sith (as well as their brown robes vs. black robes) and the silver and red of the Rebellion vs. the blue and black (and white) of the Empire.
Toy Story 3: Blue is safe (Andy's room, the Butterfly Room, the conveyor belt off switch), red is unsafe (Caterpillar Room, Lotso, incinerator), and sickly green-yellow is corrupted (the vending machine "gambling parlor", the daycare dumpster). Bonnie's color is bright "happy" green.
FilmTraffic uses different colored filters to distinguish the various locations and storylines. For example, Mexico is yellow, while the the politician storyline is blue.
In the original Tron the good guys were typically identified by blue lines while the bad guys were identified by red lines.
Wall Street: Money Never Sleeps. All of the characters wear suits in morally ambiguous shades of grey. The villain, Bretton James, wears a demonic red suit.
Wreck-It Ralph: According to the film makers, the characters colored venomous green are the ones who are truly evil. Note that Ralph is entirely green during his Hulk-like rampage through the stands. They were going to color Vanellope that way to signify her glitch status until they figured it made her look like a zombie. You can see what she would have looked like with green skin on the sign in the bakery forbidding glitches from entry.
Ralph and Felix themselves may count. Felix is dressed in mostly blue, the color for peace and serenity, while Ralph is dressed in mostly red, the color for intensity and anger.
Also, whenever Vanellope glitches, she turns shades of blue. However, Turboturns shades of red when he is forced to glitch out.
As a general rule, absent any other cues like dialogue or geography (and often enough even with them), a rising sun is depicted as red and a setting sun as orange in all films. This is just a cinematographer's convention that's gone back to the early days of color film.
In the film version of West Side Story the two rival gangs have different colors to identify them - the Jets (the Caucasian gang) predominantly wear blue, brown and gray (with some yellow) while the Sharks (the Latino gang) predominantly wear red, black and purple (with the occasional pink thrown in here and there).
Folklore and Mythology
If an animal is important and doesn't have extra features (Pegasus, Sleipnir, Cerberus), it will most often be a certain color. White is a particularly strong giveaway, as many cultures believe that white animals have magical properties.
This is addressed (or lampshaded or something) in GURPSInfinite Worlds, which lists being entirely white as one of the signs that an animal may be a parachronozoid (in-world jargon for "naturally capable of moving between worlds").
Used in Animorphs. Andalite technology tends to be based around the colors blue and white. Yeerk tech (at least that used by Visser Three) is usually black and red.
In Dragonlance, the Towers of Sorcery actually enforce this trope. White represents good, Black evil, and Red neutral. This is partly because the world's history has shown a need for balance between these moral axes. Extremes of corruption and piety have brought ruin to the world.
Subverted in one Dragonlance short story. A knight slays what he thinks is a white dragon, which are Always Chaotic Evil. It turns out, however, that the dragon in question was an albino silver dragon (silver dragons are Always Lawful Good).
In Dragonriders of Pern, the dragons are visually distinguishable by gender and caste by their color. Additionally, many of the disciplines have a distinctive color that members of the guildhall wear. Miners, crafters, harpers, and healers each have a distinctive uniform color, with further variations in tone for apprentices, journeyman, and masters.
"Harap Alb", a Romanian folk tale, has the Green and Red Emperors. While Green is a wise, old ruler and the protagonist's kindly uncle, Red is a cruel, unstable tyrant, against which the protagonist is warned:
Harap Alb's father: Beware of red-haired men and especially the bald.
In folkloric context, both baldness and red hair are traditionally considered bad omens placed by God to mark dangerous men.
In the Harry Potter books Tonks favours her hair bright pink (she can change her appearance at will). In the film of Order of the Phoenix it was changed to purple because the filmmakers had already associated the colour pink with Umbridge. Interestingly in the books Umbridge didn't wear as much pink as she does in the film though it was obviously done to emphasize the Tastes Like Diabetes effect.
In Harry Potter and the Order of the Phoenix, the Weasley twins describe to Harry one of their inventions - a Puking Pastille. Biting its orange end will make you vomit, and biting its purple end will make it stop.
Most religions in the LiavekShared World anthologies are identified by color: red for the Way of the Twin Forces, black for the Kin of One Path, white for the Church of Truth, green for the House of Responsible Life, and brown for the Pardoners. There are two more color-coded religions — blue and gold — that have been exiled from Liavek, and one non-colored religion, the Way of Herself. The clergy of any religion are almost always called (Color) Priests.
Used in Orphans of Chaos. When using her higher senses, Amelia can see the utility of nearby objects to her or someone else by how brightly they glow with a white light.
The Reynard Cycle: In Calvaria, you can instantly determine anyone's general profession and rank in society based entirely on the color of their clothing:
Children, and people of the service class, wear white.
Artisans, engineers, and laborers wear tan.
Members of the military wear gray. Non-Calvarians sometimes refer to all Calvarians as "the Grays" due to the fact that they've never seen one who wasn't a soldier of some kind.
The blood-guard (Calvaria's State Sec) wear black trimmed with red.
The Judges (the law makers and arbiters of justice) wear red trimmed with black.
There was a series by Garth Nix called The Seventh Tower featuring a caste system based on the rainbow; the more powerful a particular color in the society's magic system, the higher the rank of the corresponding caste. Everyone owned a crystal with which they could perform light-based magic; any individual could use colors and visit floors of the complex (in which the entire society lived) equal to or lesser than their own rank, but needed special dispensation to go higher in the pecking order without actually going to the trouble of earning an increase in social station. In the lowest floors was a caste of servants who weren't given a color at all, who were regarded as being not wholly dissimilar to lepers.
The Stainless Steel Rat's Revenge. The planet of Cliaand is completely militarized and every person on it has a uniform with a color appropriate to their job.
Lampshade by Diana Wynne Jones in The Tough Guide to Fantasyland, wherein she explained that a Genre Savvy character can always identify which characters are (or will turn out) good, evil, traitorous, possessing magical powers, or lost royal heirs upon first meeting them by the color of their hair or eyes (or combination thereof).
Live Action TV
Awake: Has two realities, with the tone of the camera distinguishing them for the audience and a colored wristband distinguishing them for the protagonist.
Played for Laughs briefly, when Paige in Season 5 tries to colour-code the pages of the Book of Shadows with sticky tabs for more efficient research. Piper is not amused.
Piper:(ranting) "Beings of evil are red, creatures of good are white." Oh, yeah? Well, what's a Bunyip? Because it's not good or evil, so what the hell color is that? (finds the page with a red and white tab) Oh. Well that's confusing.
In the season one episode "Which Prue Is It Anyway?", Phoebe tries to color-coordinate a trio of Prues.
Clue: The main cast members usually wear something of "their piece"s color.
Criminal Minds: There is an in-universe example in the episode "Magnificent Light". The bad guy is a man suffering from synesthesia, a neurological condition where two different senses are experienced at the same time. He can actually see the words as they are spoken by someone else and the colors in which these words appear to him indicate if the person is good, evil or even a liar. In his case, white means good, red means evil and orange means deception.
Degrassi: Community School introduces uniforms in Season 10 of the eponymous show, color-coded by year (Grade 12-blue, 11-red, 10-purple, 9-yellow). This holds the next year, apparently for the viewers' convenience - in a real school, it would make more sense for the rising students to keep their present colors with blue rotated to the incoming freshmen.
Because the TARDIS is blue, that colour is often associated with the Doctor, especially the Tenth, who wore a blue suit as often as his brown one and whose sonic screwdriver had a blue light.
The Fourth Doctor's coat would change depending on the "genre" of the particular serial. The yellow-brownish one was more for adventure, red for action, and grey for horror or mystery.
In the Fifth Doctor's first season, the boys are in yellow and the girls are in purple.
As the 7th Doctor was growing Darker and Edgier his coat is changed from a light whitish colour to dark brown.
Since the Ninth Doctor, the time vortex is blue if the TARDIS is going backwards in time, and red if it is going forward.
The Doctor's bowtie in his eleventh incarnation will be red if the episode takes place in the future, and blue if it's in the past. Also, his coat, much like the Seventh Doctor, is a much darker brown after the events of "The Angels Take Manhattan".
The Daleks have been traditionally color-coded according to their positions in the Dalek hierarchy: The armor of leadership-level Daleks was usually distinguished by black, gold or chrome markings, with the Supreme usually being predominantly black in color. The Emperor's Guard typically had black domes, while Dalek Sec - the leader of a secret order known as The Cult of Skaro had an entirely black casing. In 2010, a new hierarchy was introduced:
Scientist - orange
Strategist - blue (later a darker, metallic navy)
Eternal - yellow
Supreme - white
Officer-class Drone - red (later a darker, metallic burgundy)
Standard Dalek - bronze
When they were divided into two factions in Remembrance of the Daleks, they had different colors as well.
Fringe: The opening credits distinguish which universe the episode is in. Blue=our universe, red=parallel universe, amber= rebooted and connected universe.
This is how the universes came to be called the "blue-verse" or "red-verse" by fans.
Gray signified time jump episodes.
Game of Thrones: The families are colour coded by hair. The Lannisters are blonde, the Baratheons are black-haired, the Targaryens are platinum, the Greyjoys are light brown-haired and the Tullys are reddish brown-haired. This is a blessing to the viewer trying to keep track of the Loads and Loads of Characters, where the politics between families is the main theme.
Grey's Anatomy: Scrubs colors within Seattle Grace: Light blue = intern/resident, dark blue = attending, turquoise = nurse, peach = dermatology. To identify people from other hospitals: orange = Mercy West, red = Seattle Presbyterian.
Merlin: Merlin and Arthur usually wear blue and red respectively, as a near-literal example of Red Oni, Blue Oni. Spirited Young Lady and Rebellious Princess Morgana wears bright, jewel-like colours such as reds, blues, purples, and greens, whilst the gentler Shrinking Violet Guinevere wears almost every shade of pastel imaginable: lavender, peach, pink, and light blue. By series four, the bad guys (Morgana, Agravaine, Helios, and Shade!Lancelot) wear black, whilst those with magical powers are usually delinated by the colour green, particularly Mordred and the other Druids, who wear green cloaks.
Power Rangers: Every Power Ranger will always wear at least one item in their Ranger color. Former Rangers will usually dress in neutrals like black, gray or brown. Family members or love interests of specific Rangers will also often dress in their relevant Ranger's color. Every now and then, you'll get a side character, like Emily in Zeo, who dresses exclusively in orange.
On TNG, Cadets wore a variation on the standard uniform, but with the colors reversed: division-colored shoulderpads on black jumpsuits. This later became the attire of "lower deck" drones who labored within space stations and other departments; no glamorous Galaxy-class explorers, they. Cadet uniforms are usually grey, although they too underwent changes.
Also for many of the major races and nations, who are associated with particular colour schemes:
The Federation is a rich blue (on star charts, on their seal, in their warp plasma) supplemented by other light pastel shades and grey (for ship bulkheads).
The Klingons are red (on star charts, on their banner, their graphic displays and ship controls, their warp plasma, their transporter effect). They also prefer red lighting aboard their ships and in their buildings.
Romulans are deep green (on star charts, on banners and display graphics, their warp plasma, their transporter effect). Their ships also have a deep green hull colour.
Interestingly Romulans have green blood (copper-based). This means the ships are blood colored.
Cardassians are usually yellow-ochre or pink (both colours were used for their weapons - pink in their first few appearances, later yellow, their transporter is yellow-ochre, on star charts they're either yellow or pink). Their ship hulls are ochre. Their graphics and display panels use orange/beige and green, colours that sometimes appear on their cultural emblem.
The Dominion is purple (their warp plasma, on star charts; their graphics are purple and green).
Ferengi warp plasma and ship hulls are orange.
Andorians, to no-one's surprise, like white and blue, along with a pale beige.
The Borg favours black and a sickly green.
Bajorans uses gold-tan and dark red.
Japanese idol group Momoiro Clover Z wears different colors for each members and match to their gimmicks, also acts an shout to Super Sentai.
K-pop group Rainbow has seven members, each corresponding one of the colors of the rainbow.
Supertramp's Album Crime of the Century has this. The lyrics sheet is color coded for each of the two singers. Roger Hodgson is white, and Rick Davies is yellow.
The targets for the racers in Banzai Run correspond to their own colors and names.
Indiana Jones (Stern) uses different colors for each of the four films: Last Crusade is blue, Temple of Doom is red/orange, Raiders of the Lost Ark is yellow, and Kingdom of the Crystal Skull is green.
Indianapolis 500 uses orange, yellow, blue, and green to distinguish between the four main shots, assigning an opposing racer and a set of game modes to each color.
RoboCop's Prime Directives in Data East's 1989 pinball are colored red, green, and yellow; completing each directive allows the player to arrest the corresponding criminal.
In Stern's Spider-Man table, the villains' targets and indicators are color coded for each one — green for the Green Goblin, yellow for Sandman, dark blue for Venom, and red for Dr. Octopus.
In Transformers, the various characters and indicators are color-coaded for the corresponding factions, using "Decepticon violet" and "Autobot crimson". The playfield is thematically divided into two color-coded halves, and the "Combo" Limited Edition version has each half of the cabinet similarly colored.
Sega Pinball's Starship Troopers uses different colors to identify the various Bugs that need to be destroyed on each planet — yellow for Warriors, blue for Plasma Bugs, green for Hoppers, and red for Tankers.
The Four Pillars of Pro Wrestling/All Japan Pro Wrestling in the 1990s each had a signature color: Misawa was Green, Kobashi was Orange, Kawada was Yellow, and Taue was Red. Jun Akiyama would later take on Blue.
WWE Raw is the red show, and Smackdown is the blue show.
This is in effect on a general scale in BattleTech, insofar as the Inner Sphere is considered. The 'accepted' color pattern for the five great houses is Davion yellow, Kurita red, Steiner blue, Marik purple, and Liao green. Comstar possessed no planets beyond Earth, but were associated with the color white. Later additions to the map, such as the Free Rasalhague Republic and the St. Ives Compact, appear in a shade of teal and a sort of yellow-green, respectively. When the six invading Clans appeared in the Inner Sphere, color variants became necessary. Clans Smoke Jaguar and Steel Viper received dark and light shades of gray, respectively. Clan Wolf space was denoted in brown, and Clan Ghost Bear in white. Clan Jade Falcon, naturally, received a brilliant green, where Clan Nova Cat was shown in black. While these were the 'stereotypical' colors, this did not always apply to the units from those particular factions, however.
For the longest time in Dungeons & Dragons, one could easily distinguish between good and evil dragons by whether or not they were metallic and shiny (good) or vividly monochromatic (evil). This was eliminated in 4th edition, though it still gives an idea of whether or not a dragon is more likely to be more "social" or more predatory.
Played with as early as "Basic" D&D, in which dragons still had distinct alignments by color but whites and blues were neutral, and where a later boxed set introduced more powerful similar-looking but always differently-aligned "gemstone" dragons in a rather obvious attempt to mess with expectations. (This incarnation also had only one "metallic" dragon type — gold (lawful), with its chaotic gemstone counterpart being amber).
In a meta example, New Horizon requires two differently colored twenty-sided dice. The rulebook labels them White and Black; you can only get criticals on the black dice.
In Must Be Tuesday, character sheets are adorned with a slider, one half red, the other blue. A character on the red end of the slider is well accustomed to the events of a mundane life, while a character on the blue end dabbles in the supernatural. Going too far in either direction is not fun.
Alpha Complex in Paranoia is colour coded for your inconvenience. It's almost certain that to get anywhere interesting, you'll have to cross an area outside your colour clearance. (Paint is strictly rationed and outside your clearance.)
The use of color to distinguish sides is so common that it's easier to note exceptions. For instance, in shogi, the pieces of the two sides are identical and distinguished by which way they're pointing.
Antichamber: The color of the blocks used in any given room hint at the gun required to solve that puzzle.
Ao Oni: The titular oni's bright bluish-purple colour means you will spot it the second it enters the room. Unless it's dark...
In BEMANI games, difficulty levels are almost always color-coded.
DanceDanceRevolution:note The names of difficulties have changed many times throughout the series. These are the current names. Beginner (Blue), Basic (Yellow), Difficult (Red), Expert (Green), Challenge (Purple)
BioShock and its sequel color-code the security turrets, bots, and cameras: red ones are hostile and green ones have been hacked to be on your side. The lights on the Big Daddies' suits' portholes are similar: yellow light means it's neutral, green means it's hypnotized, and red means it's hostile.
BlazBlue: The color of a super flash indicates what kind of move your opponent is about to unleash:
Cactus and Mr. Podunkian's game Dungeon uses a simple system for its Retraux graphics. The player, the walls, and all harmless decor are white. Deadly objects and enemies are red.
Enemies in Chalk have to be color-coded, as each type has vastly different way of defeating it. It also serves as a hint system for bosses, who need to be fought the same way as normal enemies of the same color.
In Crystal Story, weapons with stats that are geared towards magic have blue text, while weapons with stats geared towards melee have red text.
Donkey Kong 64 was practically built around this idea. If anything important pertained to a certain character, one simply had to look at the color to figure out to whom the task belongs. For Donkey Kong, it was yellow; there was red for Diddy, blue for Lanky, purple for Tiny, and green for Chunky.
Dwarf Fortress features dwarves that are different colors depending on their jobs, the result in your main meeting room being a mess of brown, white, grey, blue, etc. smiley faces.
In 50 Cent: Blood on the Sand, ammo pickups are colour-coded based on the weapon type—blue ammo is for close-range weapons, yellow is for machine guns, and red is for special weapons like snipers and rocket launchers. The enemies you fight are also colour-coded in this way to tell you what kind of weapons they're equipped with.
Final Fantasy X: Arguably, the stark contrast between Tidus (light hair, dark skin, heavy use of yellow and black in his clothing) and Yuna (dark hair, light skin, heavy use of white and blue in her clothing) represents the stark differences between the two.
Final Fantasy Tactics has the player party and enemy party (for humans/humanoid characters anyway) colored differently from each other so you can tell who was friendly and who was a foe; generic friendly characters are usually colored in blue and green clothing while enemy unites usually wear clothing in red and purple. The color coding concept carries on to the sequel as well.
In Forza Motorsport 4, the cars each AI driver drives are the same colour, when a car's colour can be chosen.
For instance, M. Rossi's cars are [almost] always red, as close to Rossa Corsa as possible.
Gears of War tends to give the COGs blue lights on their armor and the Locusts red.
In Ghost Trick, the colour of the ghost world varies from ghost to ghost. With Sissel, it's red, with Missile, it's green, and with Yomiel, it's blue.
In Gruntz, your gruntz are orange. Enemy gruntz cover a wide palette, each color denoting a different behaviour.
Guild Wars color-codes everything. Professions are color coded, and skills for that profession have icons of predominantly that color, and the bosses of that profession have an aura of that color, and so on. PvP and the factions in Factions use the classic red vs blue setup. In some PvP maps, they even color-code the objectives to group them!
In Hard Reset, the explosive things are colored orange, while parts of the environment that form large electrical arcs when shot are labelled cyan.
Kessen II: Once again, Shu's officers dress in Green, but Wei and Wu switched. Wei officers in this game wear Red and Wu's army dress in Blue.
In Majin And The Forsaken Kingdom, each of majin’s powers corresponds to a colour: yellow for lightning, blue for wind and orange for fire. Feeding it fruits of these colours will permanently increase the power of these abilities. Conversely, enemies that block elemental powers with their shield have a gemstone of a corresponding colour included in the centre of the shield.
Mario & Luigi: Bowser's Inside Story has several bosses and minigames where Mario and Luigi can each only deal with half of the threats—for instance, a scrolling shooter-style minigame where each of the things to be shot can only be shot by a specific brother. Mario and Luigi wear red and green, respectively, so whatever Mario targets is red and whatever Luigi targets is green.
Inside the main Mass Effect series, the Paragon and Renegage moralities are associated with blue and red, respectively. It is especially shown with endings of the games of the main series, with the colour motif of the chosen morality being displayed in it.
In Mass Effect 2, the merc groups are distinguished from one another by their armor color and the races of its members: the Blue Suns have blue armor and are staffed by humans, turians, and batarians; the Blood Pack has red armor and consists of krogan and vorcha; and Eclipse uses yellow armor worn by humans, salarians, and asari.
Likewise, the life bars are color-coded: purple for biotic barriers, blue for tech shields, yellow for armor, red for health.
Cerberus' logos and vehicles often possess an orange color scheme, while as of the third game, the Systems Alliance is represented by a blue one, likely to contrast with Cerberus. The Normandy SR-2 gets recolored as such between the games when it comes into the Alliance's possession from Cerberus, as do many of the Alliance variants of ships seen previously used by Cerberus in the second game (such as the Kodiak shuttle). Even the menus switch from blue, to orange, to blue again throughout to the trilogy to represent whatever faction Shepard is working for at the time.
Doors in the Metroid series are color-coded based on what weapon the player needs to shoot them with to open them; the standard colors are blue for any weapon, red for missile doors, green for super missile doors, and yellow for power bomb doors. The exceptions are Metroid II (the game is totally monochrome) and Metroid Fusion (colored doors work on a security-level system, and open to any weapon once you have the clearance for them).
In Bungie's Oni, hit sparks are color-coded to indicate the health of whomever is taking damage: green hit sparks represent a healthy combatant, yellow indicates having approximately half their health left, and red indicates near-death.
In Osmos, you control a primordial cell and the gameplay consists of assimilating other cells. The player-controlled cell is bright blue. The cells that are small enough to be absorbed are blue-coloured, or at least have a blue ring around them, while ones that will absorb you are red in colour.
In Pixel Dungeon, the potions follow a strict 1 color = 1 potion type code. Which means that is you have a crimson potion and it is a Potion of Healing, then you can know for sure that all healing potions are crimson and all crimson potions are healing potions
What makes it not so convenient is that you initially don't know which color is which effect, and the association is randomly set for every new game. So maybe now those crimson potions are not Potions of Healing but Potions of Liquid Fire and you should really not drink them.
In a large number of cases, Pokémon in general will ascribe to a certain colour scheme. Fire types tend to be red or orange, Water blue, Poison purple of varying shades, Electric blue or yellow, Ice white or light blue, Ghost grey, Dark black, Dragon blues and blue-greens (at least in part), Ground brown and dusty orange, Rock brown and grey, Normal brown or beige, Grass green, and Steel grey. Psychic, Fighting and Fairy are more varied in general, and Bug types often have colourful shells or wings, as real-life arthropods do, thought there are a lot of red, orange, and green Bug types, they aren't prevalent enough.
And each of the version mascots, except in Black and White, matches its version color. For the ones that aren't obvious by the name, Crystal is Purple/Light Blue, Diamond is Baby Blue, Pearl is Pink, and Platinum is Gray Red and Gold.
In Prison Architect, the colour of the prisoners' shirts determine the security level. Grey means minimum security, orange means normal security, and dark orange means high security.
In Rescue on Fractalus!, ace pilots (worth more points than regular pilots) wear purple helmets instead of the usual white. Aliens' heads are green, allowing you to tell apart real pilots and alien impostors. On later levels, however, the aliens get savvy and begin wearing white helmets.
In Resonance of Fate, weapons, damage displays, and damage is displayed in either blue or red, depending on if they do Scratch or Direct Damage, respectively.
Each of the characters' fur/feather/body color tends to follow them everywhere. An interesting case is Shadow, whose fur is Black with Red highlights: he is usually associated with Blacks and Grays or Dark Red, but for some reason, his attacks are all orange.
In the game Sonic Heroes, the twelve playable characters are divided into four teams of three members each. Each team consists of a speed character, a flying character, and a power character. Most obstacles are color-coded to tell the player which team member is intended to clear that obstacle with blue for speed, yellow for flying, and red for power. These colors are based on the fur colors of the "main" team featuring Sonic as the speed member, Tails as the flying member, and Knuckles as the power member.
The platform game Star Guard, also with Retraux graphics, uses simple colors as well. You and your allies are green. Deadly things are red.
The Lumas: White (Luma), Black (Polari), Purple (Lubba), Red (flying), Orange (Co-star), Yellow (launch star), Green (green star), Blue (Lumalee Lumabop), and Pink (Hungry Luma).
Koopa Troopas and Paratroopas: Green (walk in straight line for Troopas, hop aimlessly for Paratroopas), Red (walk back and forth for Troopas, fly up or down or side to side for Paratroopas), Blue (kicks shells), and Yellow (flashes).
Goombas: Brown (on dry land), Blue (in caves), and Gray (in castles).
Piranha Plants: Green (hides in pipes when Mario/Luigi is near it) and Red (comes out of pipes even when Mario/Luigi is near it, but will not come out if Mario/Luigi is on top of it).
Cheep Cheeps: Red (faster, can jump out of water) and Gray (was changed to green in All Stars, slower, always in water).
Bros.: Lime (Hammer), Blue (Boomerang), Red (Fire), Green (Sledgehammer), Purple (AFHB), and Orange (Sumo).
The characters in Team Fortress 2 work for two companies called RED and BLU [sic]. It's no coincidence that the Administrator and her assistant both wear purple. Even with all the unlockable weapons and modifiable accessories, the game has never allowed you to wear the colors of the opposite team (not counting disguised Spies).
In the Tomba! series, Items are split into 3 colors in the select item menu: Green, Blue, and Pink. Green Items are equippable weapons and clothes. Blue items are regular items such as the Buckets and lunch boxes. Pink Items are special automatic use items such as the Evil Pig Bags and the Treasure Chest Keys that can only be used by talking to the right NPC or doing something in the right location.
Tomb Raider III: The Save Crystals for the PS1 version emanate a bright blue light, making them extremely easy to spot from a distance and during the darker portions (which there are a lot of) each level. They can even be seen from the other side of walls they are placed too close to.
Touhou games have red items for power, blue for score, green for Smart Bombs (except in 10 and 11, where bombs were tied to power, and green items increased the value of blue items), and purple for extra lives.
After Mountain of Faith, red fairies give you power, and blue fairies give you points.
In Trauma Center, there is a type of GUILT called Tetarti. It can come in groups of 3 with three, four, or five colors. Their color is shown when they appear and then they turn gray. To kill them, you must inject each one with the serum that has the same color.
In the Vietcong series, anti-communist forces will always wear camouflaged (ERDL/Tigerstripe), lime, or brown uniforms while the NVA wears dark green and tan uniforms. Some VCs in the first game (or all of them in the second) wear black pajamas.
In the Wing Commander series, Terran Confederation fighters are generally painted in bright colors, typically silvers and greens for the first two games and bright grey for the remaining (except for the Excalibur and Dragon superfighters, which have dark-colored hulls). Kilrathi fighters are generally ochres and darker colors. And Border Worlds Militia fighters are gunmetal grey.
Largely averted in Wizorb. The multi-coloured blocks and boxes will usually drop different things depending on the part of the level they're in. This includes the Poison Mushroom items.
In World of Goo, different species of goo balls have different colour. It'll be difficult to tell them apart without this.
In The World Ends with You, it would be easier to list the things that AREN'T using this trope. The most prominent use of this trope comes into play when scanning for Noise. Red symbols are your typical encounter, orange symbols are usually tied to a mission objective, green are Pig Noises, blue are Boss Noises (which only show up in the post-game), and black are Taboo Noises. Black symbols will also float towards you in order to start a battle.
In XCOM: Enemy Unknown, the type of a weapon can reliably be known by the color of the blast. Firearms are brownish white, lasers are always bright red, and plasma is always bright green. (There are a few other weapons that don't fit this scheme, most of them are white or gold and are uncommonly powerful.) It is of course completely unrealistic (bullets are not visible with the naked eye, lasers that would be suitable as personal weapons would probably be infrared and therefore invisible, and plasma is just very, very hot stuff so it would appear a very bright blueish white should it somehow be weaponized.)
The Black Brick Road Of OZ's witches all have a corresponding color which they seem to share with the Country they rule (for example Pepper's color is yellow and Bastille's is violet).
Homestuck: A bunch of things have associated colours:
Celestial Bodies - Derse has purple, Prospit has yellow, Alternia's moons are green (tied to the felt) and pink. The Green Sun is the same shade of green associated with Lord English. The Cherubs' planet is colored red by a red sun.
Groups - The armies of Derse and Prospit have black and white respective due to Chess Motifs being in effect; the Felt (including Doc Scratch and Lord English) all have the same shade of green.
Realities - Kids' and Trolls' universes respectively are depicted as red and blue (a motif tied to Sollux's bifurcation quirk and red and blue eye/ glasses). Different versions of Sburb in different universes are different colors as well, green for the pre-scratch Earth, purple for Alternia, and red for post-scratch Earth.
Once the game in Larp Trek begins in earnest, out-of-character panels have a grey background while in-character panels have colored backgrounds. Each character is eventually given a single, consistent color, too.
In Nimona the good knight Goldenloin wears a majestic gold and white armor while villain Blackheart dons black and red. (In reality, their roles are not that simple.)
Schlock Mercenary gives us an in-universe example, with Lt Shodan's suspicion that a bunch of new recruits charging ahead and blazing away with their guns were prevented from shooting one another only because they were wearing the same color.
Starting in the second volume of Serenity Rose, important characters have coloured hair in the otherwise mostly black-and-white comic. Furthermore, sorcery is generally coloured to show that it is abnormal to the world around it and also to help identify who made it.
Sera has Blue hair and stuff she conjures up is usually green.
Vicious has bright pink hair and her magic tends to radiate a matching shade.
Stiletto has orange hair and her magic is blood-red
Tess has bright red hair, and is so far the only non-witch to have such an eye-grabbing colour.
The lead characters in Bite Me! are always dressed in the primary colors, Mike, Jeff, and Greg in yellow, blue, and red respectively.
In Elcenia, dragons' colors indicate their magical abilities. In addition to breathing fire of their color, reds gets improved firebreathing and fire resistance, greens get magical empathy, blues are better shapeshifters, violets can breathe underwater, blacks get improved senses, and whites fly better.
The villains of the show "Cheat Commandos" from Homestar Runner are actually named Blue Laser.
Franz Hopper - White. Also used for inactive towers on Lyoko in later seasons, which is either a continuity error or Fridge Brilliance.
Dexter's Laboratory - Mee-Mee and Lee-Lee (Dee-Dee's friends) wear green and purple versions of her outfit.
G.I. Joe - The good guys shot red laser beams and the bad guys shot blue ones. If a good guy picked up a bad guy's weapon and started firing...it would switch colors.
Anatomical diagrams traditionally use red for oxygenated blood vessels, blue for deoxygenated blood vessels, yellow for nerves, and green for lymphatic vessels. Can give rise to Reality Is Unrealistic, as some would-be med students take these colors literally and are later shocked to learn that actual deoxygenated blood is maroon, lymphatic fluid is clear-to-milky, and nerves are white.
Artificial flavoring in the U.S. tends to follow a set pattern somewhere between this and Tastes Like Purple for things that are flavored, such as Popsicles, fruit drinks, or candy.
Yellow = Lemon or, less frequently, Banana (occasionally Pineapple)
Green = Lime or Mint, very occasionally used for Apple.
Blue = Blueberry or Blue Raspberry.
Purple = Grape
White = Pineapple, Coconut
Cigarette packaging tends to follow a general color-coding scheme, although it's far from universal. About the only thing that's consistent across most brands is that if it's in a green or predominently green pack, it's menthol.
Red = full flavor
gold or blue = lights
silver or white = ultra lights
green = menthols
Dairy product labels:
In the US, Whole milk is almost always red. 1% milk is usually light blue, 2% dark blue. Skim milk is usually yellow. Half-and-half is usually purple. Chocolate milk is brown.
In New Zealand (the world's largest milk exporter), whole milk is dark blue, low fat is light blue, and skim is green. Non-homogenised milk is silver, calcium-fortified milk is yellow or orange, and cream is red. Like the US, Chocolate milk is brown.
Even cheese is color-coded in New Zealand - cheddar ("tasty") cheese is red, colby is yellow, edam is blue, mild cheese is light green, and mozarella is dark green.
Electrical components such as resistors and transformers generally follow a (rather complex) color-coding scheme - the more bands it has, in the case of the Resistors, the higher ohms its resistance is, and the individual colors are multipliers for the base number, as seen here.◊
Fruits change colour depending on how ripe they are. This is thought to be why humans evolved colour vision in the first place. Additionally, recent studies have shown that women see far more different shades of color than men (where a man will see "beige," women will see beige, tan, bone, ecru, and several other shades that men don't). They believe this is a holdover from the old caveman days, when women were the gatherers and had to differentiate between "safe to eat" red berries and "highly poisonous" red berries.
The "Hanky Code", a series of signals supposedly used to indicate kink and gender preferences in bars. The color of the hanky indicates the activity and the position of the hanky (left or right back pocket) indicates a dominant or submissive.
The "hoods" (more like shawls) worn by US college faculty at graduation ceremonies are doubly color-coded: the velvet collar's color indicates either Doctoral status or the wearer's field of study, while the interior fabric displays where the faculty member's own education took place.
In other countries, there's a whole world of other complexities - see the Other Wiki's page on Academic Dress in the UK for example.
If you take a look at your local hardware store in the powertools section, you'll likely notice a whole rainbow of colours, usually associated with their own brand:
Black & Decker=Orange
In American politics, Blue is the color associated with the Democratic Party (liberal), Red with the Republican Party (conservative), and Green with Independent or Third-Party candidates. Hilariously, this color scheme is completely arbitrary: it was invented by the NBC broadcast network during their coverage of the extremely-close 2000 Presidential election purely as a means of keeping things straight on their electoral map. But it's been pretty much adopted by the political parties involved ever since (you'll often hear of a solid Republican or conservative state referred to in discourse as a "Red State", etc.). Even more hilariously, this color scheme is almost the exact opposite of that of European politics, where Blue is associated with conservative movements and Red with social democratic, socialist and communist ones.
In Elizabethan England, the actors on stage were color-coded - rather than wear costumes fitting the era/location the play was said to take place in, modern-day outfits of different colors were used to tell whether a person was a ghost, wealthy man, etc. This made it easier for less-educated people to understand what was going on.
In Europe, where most of the older flags are just of one or two colours, republican and democratic movements had a tendency to use striped tricolours as their flags. The first such example was probably the flag of the Dutch provinces rebelling against Spanish rule in the 16th century, which is used to this day and is striped horizontally red (originally orange), white and blue. The abortive Belgian Revolution of 1788 used the colours black, yellow and red. The French Revolution combined the red and blue of the city of Paris with the white of the Bourbon dynasty, resulting in the vertically striped blue, white and red flag of today. As the revolutionary armies moved beyond the borders of France, they founded new republics with different tricolors, for instance green, white and red in northern Italy (now the national flag of all Italy) and green, yellow and red in the Helvetian Republic (when that became Switzerland again, they reintroduced their old bicoloured flag). Other such "radical" tricolors were the black, red and gold (yellow) flag of the German revolution of 1848 and the red, yellow and purple (claret) flag of the Spanish Republic used until it was crushed in the Spanish Civil War.
International auto racing, prior to the rise of sponsorship liveries in The Seventies, although national colours are often still incorporated into these liveries, and are also usually offered on road cars.
Gray or silver = Germany, still used by Mercedes Benz and Audi.
Dark Green = UK, usually called British Racing Green, used by Aston Martin in sportscar racing, and Caterham in F1.
White stripes over Dark Blue = USA, often still available as an option on sports cars.
White and red = Japan
Yellow - Belgium
International political movements are often associated with specific colors. Although it can vary from country to country and from time period to time period, broadly speaking:
Red: the color of blood, passion, and revolution, Red is usually associated with populist, radical, and occasionally violent, political movements. Nowadays most commonly associated with Marxism and Communism, but in the past a wide range of radical political movements claimed Red as their color (most famously the Red Shirts of Garibaldi's volunteer army).
White: color of purity and peace. Nowadays mostly associated with Pacifism.
Beginning in the 18th Century, White was associated with loyalist or monarchist factions during civil wars, e. g. the white cockade of the Jacobites, and the white badges and flags used by Royalists during the French Revolution and by the "Whites" of the Russian Civil War. Hence, White becomes associated with the reigning monarch, and Red with the rebels seeking to overthrow that monarchnote However, this is in part coincidence, result of the Bourbon dynasty's long association with the colour white (going back to Henry IV's white plume) and the fact that Czarist armed forces had been using white flags with a blue saltire since the middle ages..
Black: Politically, the color Black has a long association with anonymity, lawlessness, and "non personhood." Where colors or patterns of colors would signify personal identity and political allegiance, solid black, as the absence of color, meant the absence of allegiance. As far back as the Middle Ages, "black knights" carried no family crest or color on their shields, symbolizing their independence (or simply concealing their identities). Beginning in the 19th Century Black was adopted by Anarchist groups: the color of no country or government. More radical Anarchists groups often also use Black in conjunction with Red.
Black is also the colour of the vestments of Catholic clerics and by extension is associated with Catholic and Christian Democratic parties in various European countries.
Black is also a colour strongly associated with Fascism, from the proverbial Black Shirts of Mussolini's followers and their British imitators, to the black uniforms of the German SS.
Brown: After World War One, Brown became the color of Nazism. Nazis party officials and most of its organisations (except the SS and some of youth organisations) wore brown uniforms - the first ones had been surplus army shirts intended for use on the Turkish fronts (note that the regular German and Austrian army uniforms in the war had been in different shades of grey). The Nazi party central office in Munich was known as the Brown House.
Green: color associated with nature, Green is the color of most Environmentalist movements.
Green is also associated with Islam in many places.
In Ireland it is often seen as the colour of Nationalism and Catholicism, as opposed to Orange, the colour of Loyalism and Protestantism.
Gold: the "color of money," associated with Free Market Capitalism, and sometimes, by extension, Libertarianism.
Purple: In modern European politics, Purple is usually associated with coalition governments, being a combination of Red (radical left) and Blue (traditional conservative).
Purple is often associated with royalty, as it was the color worn by Roman Emperors. By extension, Purple was also associated with the Catholic Church during the Middle Ages.
Pink: associated with LGBT and Women's Health movements.
In Organized Labour circles, Pink has negative connotations, being a lighter shade of Red and therefore associated with moderate or "soft" socialism. The epiphet "Pinko" was coined during the first Red Scare of the 1920's to imply a person had socialist leanings without actually being a member of any organization or political group.
Many military forces will have particular colors they are associated with (for instance, the Red coats that the British army wore for some time). In modern times, said colors can distinguish between branches of a nation's military or, in some cases, smaller branches within those branchesnote the United States Army, for instance, has certain color-coded bits on their service uniforms to distinguish members of the different corps; for example, the Military Police Corps wear green and gold, while the Signal Corps wear red and white.
In 1940, when the risk of a German invasion was at very high, the Irish army switched their uniform color and helmet style (which, at the time, were similar to Germany's) to emulate Britain's, so they would be readily identifiable as neutral troops and not enemies from a distance by British soldiers.
With a serious possibility existing that the Germans would invade Ireland as an easier alternative to directly attacking Britain, having Irish troops patrolling a border with nervous British soldiers on the other side primed and ready to recognise German equipment, this was held to be too big a risk, and the Irish adopted British -style helmets.
Many screwdriver or plier sets have the handles color-coded by tool type (for example, all flathead screwdrivers will have yellow handles while all Phillips heads will be blue) so that you can tell what type of tool it is at a glance.
Many space-filling or ball-and-stick models of certain molecules will have certain elements given a specific color. Here are some examples:
Hydrogen = white
Carbon = black
Nitrogen = blue
Oxygen = red
Fluorine = dark green
Sulfur = yellow
Chlorine = light green
Many street gangs have one or more colors associated with that particular gang. For example, the Crips are blue and black and the Bloods are red and black. This can lead to hilarity of the deadly type for people who wander into gang territory wearing a rival gang's colors, intentionally or not.
Most moist snuff brands follow a certain pattern on their labels:
red (ranging into brown) for "Natural" or "Straight" flavors
green for Wintergreen flavors
blue for Mint and "Ice" flavors
One brand even has a "cool wintergreen" packaged with a bluish-green label. The fruit flavors offered by some companies tend to break this a little.
Most sports teams have one or two colors associated with their logos/jerseys. In international competitions (World Cup, Olympics), it almost always overlaps with National Colors.
In soccer matches, however, this is oftentimes subverted. Italy, for example, plays in all blue, although Italy's National Colors are Green-White-Red. Germany's classic dress is white shirt, black shorts, and white socks, whereas the National Colors are Black-Red-Gold.
In these cases, there's usually a historical reason behind it. Italy's national team wears blue because blue was the color of the House of Savoy, who ruled Italy when the team was first put together. The same is true of the Netherlands - their flag is Red-White-Blue, while their teams' kit is orange because they are ruled by the House of Orange. Germany's white and black outfit is derived from the Prussian flag of the 19th century.
O-type stars= blue
B-type stars= bluish-white
A-type stars= white
F-type stars= yellowish-white
G-type stars= yellow
K-type stars= orange
M-type stars= red
brown dwarfs= maroon
neutron stars= purple
black holes= black
On military ships, the colors of pipes indicate their contents
red = fire main (sprinklers/fire hose)
blue = potable water
yellow = fuel oil/gasoline
green = salt water
One aversion in real life that's still played straight in fiction: Gemstones. While in real life, most gems have the ability to be a variety of colors, in fiction, they still follow a pretty set pattern:
Diamonds = Clear/White
Emeralds = Green
Rubies = Red
Sapphires = Blue
Topaz = Yellow
Amethyst = Purple
The PC99 standard gave us the color-coded ports and plugs we all use today to tell the difference between identical plugs that go into identical sockets with different uses (e.g. headphone and microphone jacks, old PS/2 keyboards and mice, etc.).
Pre-Communist political offices were identifiable by color, the pattern on their uniform, and the fanciness of their Nice Hats.
The Québec student strikers of 2012 adopted the Red Square as their symbol against the 75% hike in tuition and in favor to the strike. As it gained in popularity both in the student body and the general population, other factions in the conflict tried to promote their own squares, with varied levels of success...
Some students wore the Green Square to show support for the hike and taking a stand against the strike;
Other students wore the Blue Square, which meant they were against the hike, but were also against the strike;
At some point, columnist Richard Martineau suggested the Yellow Square, which meant that you would favor a smaller hike. It never caught on. In fact, the Yellow Square already had a significance before (though perhaps not publicized enough) as anti-nuclear stand in the province of Québec.
As the conflict dragged on, some parents and teacher adopted the White Square, urging both the government and student unions to compromise with a moratorium on tuition hikes, until such time as we could discuss the matter with cooler heads.
When the government passed bill 78, which would restricts freedom of assembly, protest and picketing, especially on or near university grounds, writer Normand Baillargeon suggested the Black Square (to be worn WITH the Red Square) in protest of the violent repression suffered by student strikers since the beginning of the conflict, and as a symbol of grief over the death of democracy.
Russians with Rusting Rocketstakes it to eleven with colour-coded undershirts. No, seriously. It started back in XVIII century, when sailors traditionally wore striped undershirts (telnyashkas) and so did the naval infantry. Their stripes were either deep-blue or black. Everybody knows that sailors are Bad Ass and marines are even more badass, so when, after World War II, airborne corps were created, they received light-blue-striped telnyashkas. The first commander of airborne corps, Vasiliy Margelov, was a former marine, you see. Then, around 90's, the idea got around that you cannot be badass if you don't have telnyashka, so various forces started to introduce their own colour schemes.
Sailors: Black stripes
Naval Infantry: Dary blue stripes
Airborne troops (VDV): Light blue stripes
Border guards: Green stripes
Ministry of Interior (MVD): Red stripes
Emergency Control Ministry (Emercom): Orange stripes
Soldiers do not wear a striped telnyashka—their undershirts are white.
Similarly, electronic components are color coded so electricians can tell their power and tolerances at a glance.
Similarly to the Russian undershirts, the US Army and US Air Force have color-coded berets to differentiate between particular corps or specialties:note or at least, the Air Force does for those people who have earned the right to a beret
Pewter for Special Operations Weather Techniciannote How do the flyboys know what the weather will be like over their target? These guys sneak into enemy territory and get the weather forecast for them.
Sage Green for SERE (Survival, Escape, Resistance and Evasion) Specialists
Some high schools colour code the uniform shirts based on student's ages . See also the Degrassi example above.
Some types of medication, particularly those that are to be taken on an on-again/off-again schedule like some birth control pills. It's easier for the person to take a pill every day than to try to remember how many days they have already skipped/still need to skip so the meds are packaged with placebos for the skip week; those pills are a different color to the actual pill.
Sweetener packets for coffee and tea are often color coded: white for white sugar, brown for brown or raw sugar, pink for saccharin (ie. Sweet-N-Low), blue for aspartame (Equal), and yellow for sucralose (Splenda). Newly-developed Stevia-based sweeteners are usually coded green, and monksfruit-based sweeteners are coded orange.
This is quite common for any metropolitan mass transit system that's extensive enough to have multiple lines, although it's a toss-up whether the residents of a particular city call the lines by their colors or their actual names (assuming they have other names; some just pick a colour and use that as the name).
The vast networks of pipes in theGoogle datacenters are colour-coded, similar to the shipboard pipe example above. Similar schemes are probably in use all around the world, with network and power cables as well as pipes. Anywhere there's a mess of cables or wires, someone is probably going to make use of this concept to help make things easier to manage.
While United States dollar banknotes/bills are all green, most currencies make each banknote of a different color to help distinguish them.
Blue = 20 Euro, $5 Canadian, $10 Australian, $10 New Zealand
Brown = $100 Canadian
Green = 100 Euro, $20 Canadian, $100 Australian, $20 New Zealand
Grey = 5 Euro
Orange = 50 Euro, $5 New Zealand
Pink = $5 Australian
Purple = 500 Euro, $10 Canadian, $50 New Zealand
Red = 10 Euro, $50 Canadian, $20 Australian, $100 New Zealand
Yellow = 200 Euro, $50 Australian
When Australia and New Zealand decimalised their currencies in 1966-67, replacing one old pound with two new dollars, the colors on the pound banknotes were reused on their dollar equivalents to ease the transition. For example, the blue £5 notes in each country were replaced with blue $10 notes.
During the early 20th Century, the United States developed a series of war plans to outline what would be done in the event of a war with other countries. Some plans were more developed than others, depending on how likely the Yanks with Tanks thought war with that country was. Each belligerent was referred to by color for both brevity and diplomatic considerations - in time the plans themselves were referred to by color. For fun, try to guess whom the plan involved:
War Plan Black: War against Germany, specifically the German Empire. The most well-known involved a World War OneWhat If? where France was defeated by Germany in Europe and the latter attempted to seize French possessions in the Caribbean or launch an attack on the East Coast - the plan involved heavy mining of the seas and concentrating the Atlantic fleet in New England.
War Plan Blue: The US. No, not a prospective revival of the Confederacy - these just covered normal preparation actions to be undertaken in peacetime. In all the war plans, the US was code-named "Blue".
War Plan Brown: Dealing with an uprising in the Philippines, at the time effectively an American colony.
War Plan Gold: War with France. Much of it focused on France's Caribbean possessions rather than going all the way to Europe.
War Plan Gray: Two different ones, depending on the time period. The first was a military venture in Central America or the Caribbean - not that unlikely given American intentions of keeping the Western Hemisphere under its lead (and out of Europe's) goes as far back as the Monroe Doctrine. The second was for an invasion of the Portuguese Azores during the early part of World War II - Portugal was officially neutral but there were fears that Salazar might allow Nazi Germany to use the islands as a base to launch raids in the Atlantic.
War Plan Green: Invading Mexico, specifically to help establish a pro-American government in case of civil unrest.
War Plan Indigo: Invading Iceland, something the US actually did in 1941 (before the US and Nazi Germany were at war) after the fall of Denmark in order to allow British forces to move elsewhere.
War Plan Orange: War with Japan. This was the most extensively developed and redeveloped of the color war plans. While the main basis of it (mustering up the Pacific Fleet and confronting the IJN head-on with a large surface navy before moving on the Home Islands) became outdated with technological advances in submarines and especially aircraft carriers (before and after the attack on Pearl Harbor), elements of this plan was eventually incorporated into the US's strategy in World War II, such as the large submarine fleet that was to blockade the Home Islands (originally to buy time for the Pacific Fleet to mobilize) and not straying too far from land-based (the "island-hopping" strategy).
War Plan Purple: Invading a South American country.
War Plan Red: War with the British Empire. The largest components of the Empire got their own shades: Britain itself was "Red" (this included Newfoundland, which at the time was separate from Canada), Canada was "Crimson", India "Ruby", Australia "Scarlet", New Zealand "Garnet", and Ireland "Emerald". The bulk of this plan outlined a multi-front invasion and occupation of Canada while the US Navy blocked the Royal Navy from entering the Western Atlantic.
War Plan Red-Orange: A two-front war with both the British and Japanese Empires, which became a concern after two formed an alliance prior to World War One. It was considered a nightmare scenario for the US, as both would have brought very formidable navies on both oceans, and the planners concluded that fighting both aggressively at the same time would have strained resources too much and so felt it would be better to focus attacks on one while playing defense on the other - it further concluded that focusing on the Atlantic would be better. This idea remained when the US entered World War II with the Germany-first strategy.
War Plan Tan: Military intervention in Cuba, at the time a US protectorate.
War Plan Violet: War somewhere in Latin America. War Plan Purple was apparently split off as the plans were developed.
War Plan White: Domestic disturbance and uprising with the United States. Much of this was developed with Dirty Communists in mind, though the plan got the most exercise in the 1932 Bonus Army confrontation in Washington. Elements survived as Operation Garden Plot, which was drafted in response to race riots that broke out in Detroit, Newark, and the Watts neighborhood of Los Angeles in the late Sixties - the operation was later used in the 1992 Los Angeles Riots and immediately following the September 11th attacks.
War Plan Yellow: War in China. Not necessarily with China (whether the Republic of China under Chiang Kai-Shek, the Communists under Mao Zedong, or any of the warlords running amok); rather it concerned itself mainly with defending American interests in Beijing and Shanghai. Yes, there are Unfortunate Implications regarding the choice of color for China (and Japan as well - what do you get when you mix red (Britain and its navy) and yellow?).
Women in the Kenyan Samburu tribe wear red clothing if they aren't married and blue clothing if they are.
The WW2 German army colour-coded its soldiers in a very thorough Germanic manner. Epaulette, collar and lapel braiding advertised a soldier's arm of service at a glance. Nearly forty colours identified soldiers ranging from veterinary surgeons to assault engineers, but among the most common were white (infantry), red (artillery), pink (panzer arm, assault guns), russet brown (recconnaissance), and black (pioneers).
Adjustable temperatures, whether by a water faucet or an air conditioner/heater, usually come in two colors; red for warm/hot and blue for cool/cold.
Many bus agencies organize their fleet by color, according to the service type.
Blue: Trunk routes, usually radial.
Green: Neighborhood circulators, primarily designed to bring riders to subway stations.
Red: Express routes.
Yellow: Orbital routes.
Orange (Officially "California Poppy"): Local all-stop routes.
Red (Officially "Rapid Red"): Express Limited-stop routes.
Blue (Officially "Business Blue"): Non-stop routes, primarily using freeways.
Silver: Metro Liner Bus Rapid Transit routes; the Orange Line and the Silver Line.