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.
Please only list examples that do not fall under one of the above subtropes.
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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.).
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).
Toy Story 3: Blue = safe (Andy's room; Butterfly room; conveyor belt off switch); red = unsafe (Lotso; the incinerator); Sickly Green Glow = corrupted (the snack machine "gambling den"; the Dumpster).
Disney's Aladdin has color motifs based on its desert setting. Blue (water) = good, red (heat) = evil, and yellow (sand) = neutral.
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 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 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.
In the Brotherhood series of films, the hero always wears white boxers, while all the other villanous characters wear black underwear.
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 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.
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 Wreck-It Ralph, the developers tell us that anyone who is colored green, they are truly evil.
Also, whenever Vanellope glitches, she turns shades of blue. However, Turboturns shades of red when he is forced to glitch out.
FilmTraffic uses different colored filters to distinguish the various locations and storylines. For example, Mexico is yellow, while the the politician storyline is blue.
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").
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.
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.
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.
"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.
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).
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.
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.
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).
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.
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.
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.
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.
As of series 5, the New Paradigm Daleks are
Scientist - orange
Strategist - blue
Drone - red
Eternal - yellow
Supreme - white
The eleventh doctor's bow tie changes color depending on whether the adventure takes place in the future(red) or the past(blue).
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 dress exclusively in their Ranger color. Former Rangers will usually dress in neutral colors 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.
Revolution: The explosive-filled log in "Soul Train" is made of considerably darker wood than the other logs in the pile. Overlaps with an inversion (in live action) of Conspicuously Light Patch.
Scrubs: The medical doctors wear blue scrubs and the surgeons wear green. Nurses most often wear pink or purple and orderlies are in maroon.
Sons Of Anarchy: While it's not prominent, the gangs display their own colours. Samcro wears a lot of blue, Mayans have green, and the One-Niners purple.
Stargate Atlantis: Uniforms are colour coded in a similar manner to Star Trek. Sciences are in blue, medical are in yellow, command is in red, and military are in black.
There's also the colours associated with each race or nation, used in their graphics, ships, transporters, banners or on star charts (the latter is expanded on greatly in tie-in materials).
The Federation is a rich blue (on star charts and their seal and warp plasma).
The Klingons are red (on star charts and their banner, graphic displays and ship controls, warp plasma, and transporter effect).
Romulans are deep green (on star charts, banners and display graphics, their warp plasma, and their transporter effect).
Cardassians are 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).
The Dominion is purple (their warp plasma, on star charts; their graphics are purple and green).
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.
K-pop group Rainbow has seven members, each corresponding one of the colors of the rainbow.
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.
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.
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.)
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.
This is in effect on a general scale in Battle Tech, 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.
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.
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).
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 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.
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.
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.
Borderlands: Anything that can be interacted with (chests, switches, quest items) has a green light or aura. Considering Pandora is a barren wasteland, greenery really stands out.
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.
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!
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.
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.
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.
In World Of Goo, different species of goo balls have different colour. It'll be difficult to tell them apart without this.
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.
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.
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.
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.
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).
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.
Gears of War tends to give the COGs blue lights on their armor and the Locusts red.
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.
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.
The platform game Star Guard, also with Retraux graphics, uses simple colors as well. You and your allies are green. Deadly things are red.
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 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 Ghost Trick, the colour of the ghost world varies from ghost to ghost. With Sissel, it's red, withMissile, it's green, and with Yomiel, it's blue.
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.
Saints Row has each gang in each game represented by a different colour, so one knows who's who on the streets.
Purple: Third Street Saints
Yellow: Vice Kings/Ronin
Red: Los Carnales/Brotherhood/Morningstar
Green: Sons of Samedi/Luchadores
Blue: Westside Rollerz/Deckers
Orange: Ultor Corporation
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.
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.
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.
Franz Hopper - White. Also used for inactive towers on Lyoko in later seasons, which is either a continuity error or Fridge Brilliance.
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.
The villains of the show "Cheat Commandos" from Homestar Runner are actually named Blue Laser.
The creators of The Princess and the Frog selected their color-palette from the three colors of Mardi Gras (gold, green, purple). Scenes immersed in nature were done in green, positively-toned scenes indoors or in town were gold-toned, and scenes of dark magic used purple: of the three, the color least common in nature.
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.
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 "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.
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.
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.).
Similarly, electronic components are color coded so electricians can tell their power and tolerances at a glance.
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.
Pre-Communist political offices were identifiable by color, the pattern on their uniform, and the fanciness of their Nice Hats.
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.
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.
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 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
The WW 2 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).
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
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
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
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.
Dairy products 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, and cream is red. Like the US, Chocolate milk is brown.
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.
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
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
Some high schools colour code the uniform shirts based on student's ages . See also the Degrassi example above.
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.
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
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
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 "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.
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.◊
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.
Women in the Kenyan Samburu tribe wear red clothing if they aren't married and blue clothing if they are.
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.
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 political movements. Most commonly associated with Marxism and Communism.
There were also the famous Red Shirts of Garibaldi's volunteer army.
White: color of purity and peace. Nowadays mostly associated with Pacifism.
Going back to the 18th century, White was often associated with loyalist or monarchist factions during political revolutions, 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 monarch. 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." As far back as the Middle Ages, "black knights" carried no family crest or color on their shields, symbolizing that they had no allegiances or loyalties to any noble or kingdom (or sometimes, that they preferred to conceal their identities). In the 19th Century Black was adopted by Anarchist groups, as the color of individualism and the rejection of traditional law and government. Anarchists 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 e. g. 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 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.
In American politics, Blue is the color associated with the Democratic Party, Red with the Republican Party, 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 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.
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.
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 nutrasweet (Equal), and yellow for sucralose (Splenda).
While dollar bills are all green, most currencies to make each banknote of a different color.