In the real world, the color range of human skin is fairly limited. We largely come in varying shades of brownish, and even the most generous will generally only give humans four distinct "colors": pink, brown, red and yellow. This is to say nothing of proper ethnicity.
This is not so in cartoons. Animators, whether they're drawing cartoon characters or building models for a video game, have the freedom to make or draw anything they want. Thus, the normal range of human skin colors needn't have any bearing on the appearance of cartoon characters. Want your characters to be blue, orange, and silver? Go right ahead! Want a dude with a purple face to live next door to a green-skinned, not-from-space babe? The freedom's all yours, pal! If the characters are Genre Blind, their unusual skin tones will probably go unnoticed. If not, this may be Hand Waved in various ways or lampshaded.
Giving your characters unrealistic skin tones sounds like a great way to avoid Race Tropes and Unfortunate Implications, doesn't it? Well, sometimes. Unfortunately, it doesn't always work like this. If a character is meant to be of a specific ethnicity, they will most likely have the "correct" skin tone for their ethnicity, regardless of anything else. It seems as if only "white people" get Amazing Technicolor Skin—everyone else is left out. Still, it's a nice thought. Isn't it?
Compare Japan, which seems to do the same thing with hair. See also Ambiguously Brown, for when the skin tones are within the realms of possibility, but not clearly "defined". Do not confuse with Amazing Technicolor Wildlife, where this trope is applied to animals. Related to Hair Color Dissonance where over time the viewer's brain might percieve the skin tone to something more realistic than it actually is.
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Anime and Manga
Zentradi in Macross (and thus the first Robotech saga) mainly have natural human skin tones, but quite a few of them have been seen to have purple, green, blue, or gray skin. In Macross Plus and Macross 7, we only see them with natural and gray skin color, and by Macross Frontier, they all have natural skin colors.
Mazinger Z: Big Bad Dr. Hell is purple. No indication why, since he's seemingly human.
All the members from the Noah family in D.Gray-Man have...well, gray skin.
That's true of the anime version. However, in the original manga color art, they're also often drawn with skin in various shades of brown.
In a lot of Japanese series, people in flashbacks are shown to have completely black skin (possibly referencing kabuki theater). Revolutionary Girl Utena, for instance, gives everyone this treatment in flashbacks.
In Star Blazers / Space Battleship Yamato, Gamilons are shown with human skin tones until the episode where humans first encounter one face to face. From that episode on, they're all shown to have sky blue skin. Members of the second season's evil Comet Empire are all a rather icky shade of olive green (except Invidia, for some reason).
In fact, so many anime extraterrestrials have blue skin that it seems to be a kind of cultural shorthand for alienness.
For inexplicable reasons, Meg's rival Non in Majokko Meg-chan has an unhealthy looking white complexion. No one seems to mind, though.
The Demon sisters from Panty & Stocking with Garterbelt, who have beet-red skin due to being, well, demons. Oddly enough, this means that Kneesocks actually turns a lighter shade of red when she blushes.
The Oni in Momo Kyun Sword are every hue under the sun, almost all unlike normal human skin tones. The fact that Onihime does have a normal human skin color is a clue to her true heritage.
Pops up occasionally in the Marvel Universe. People with gamma-radiation based powers will usually be green-skinned, the Atlanteans and Kree are blue-skinnednote though Atlantean-human offspring such as Namor tend to have their human parent's skin color, and the blue Kree are actually the minority ruling class, with "pink-skins" such as Captain Mar-Vell making up the majority of the population, and, occasionally, mutants have technicolor skin.
This got lampshaded in Exiles when, at one point, the team had two blue-skinned girls (Namora and Nocturne) and lavender-skinned girl Blink figured Nocturne's departure was because the group had too many technicolor skin tones.
In a rare exception to the "only white people are multicolored" rule, Wonder Woman once dated the Hindu avatar Rama for a while, who is very blue.
Other exceptions would be gray-skinned Apocalypse (who, as an ancient Egyptian, would be non-Caucasian) and Skin (Latino), Sunspot (who turns really black when using his power), M's brother Emplate (gray), and possibly Penance (red-skinned).
I been readin' about you, how you work for the blue skins and how on a planet someplace you helped out the orange skins and you done considerable work for the purple skins! Only there's skins you never bothered with — the black skins!
And then, some years later, reversed (in a fairly light-hearted way) when a bunch of purple- and orange-skinned aliens visit Earth to complain that GL is neglecting the rest of his space sector to look after Earth; they use the same words with the colours swapped. Poor Hal just looks to the sky in frustration.
Planet Hulk: The Shadow People are gray, while the Imperials are red.
Tintin: In Land of Black Gold, Thomson and Thompson accidentally ingest a poison which, among other effects, causes their skin and hair to wildly change colour.
When Getafix the druid becomes amnesiac, his attempts at recreating the magic potion formula end up as potions turning people into various colours (not always plain). He is thrilled by this.
Homestuck: According to Andrew Hussie, he designed the human characters to be "aracial" (meaning not designed to be any particular ethnicity). As a result of this, one mildly popular Fanon is that the pure white shade used for the main human characters is their actual skin tone; they are literally that pale.
In The Film of the Book of Coraline, Mr. Bobinsky is blue, for some inexplicable reason. The medal he's wearing indicates that he helped clean up the Chernobyl disaster, so he's appatently irradiated.
All the characters from the Land of the Living in Tim Burton's Corpse Bride are dull gray, whereas everyone in the Land of the Dead (the ones who still have skin, at least) are all bright blue.
Guardians of the Galaxy, like the main Marvel Universe, has plenty of blue, green, yellow(not just Asiatic, but yellow) and even fuscia skin to go around in the Nova Empire.
In Terry Pratchett's Strata, the heroine is able to change her skin color at will when she feels like it; two examples are silver and jet black.
In Larry Niven's Known Space universe, "flatlanders" of Earth are a technicolor population, but it's just fashionable skin dye.
Steven Erikson's Malazan Book of the Fallen has people of all colors that exist on earth, plus blue. (Which is mentioned very off-handedly and thus is very puzzling at first.)
In Monster by A. Lee Martinez, thanks to a survived basilisk bite, the titular character wakes up with a different skin color every day, accompanied by a random magical power. He keeps a notebook to track the powers that come with each color — up until he gains a measure of control over this condition with the aid of the story's MacGuffin.
Serroi, of Jo Clayton's Duel Of Sorcery and Dancer trilogies, has green skin. Subverted in that it's very unusual and marks her as an obvious mutant.
Isaac Asimov's "Forward the Foundation" has a (human) judge with faint blue skin — the color gets more pronounced when she's angry.
The Capitol and its inhabitants in The Hunger Games. They are stated to have ridiculous and freakish fashions, including body dyes.
The Uglies series hints at this in Diego. It's made clear that more 'Extreme' fashions aren't allowed in New Pretty Town but in Diego anything seems to go.
In the web-novel Domina, Simon has purple skin, while his sister has jet-black. Probably just another cosmo; no one bats an eye at it.
The human inhabitants of the moon inThe Darkangel Trilogy can have white (not pale beige), black (not dark brown), copper, amber, blue, green, teal, or purple (possibly two different shades of that last, no less) skin. They were almost certainly deliberately engineered for it.
The inhabitants of Tormance in David Lindsay's A Voyage to Arcturus have many different possible skin tones, some of which don't exist in our spectrum.
The Jewels in Captain Vorpatril's Alliance are six siblings with six different skin colors - blue, white (snow-white, not pale-white-person white), yellow, green, red, and black.
The 'Colored People' in the Xanth series. They started out as blacks accidentally immigrating from our world circa the Civil Rights Movement, and due to the rule of pun in Xanth, their kids ended up with having skin tones of pretty much every color under the sun.
In the Mr. Men series, the Mr. Men and Little Misses have a variety of colors.
Similarly, the "human" puppet characters in Avenue Q are green, blue, and orange.
Star Trek gave us blue Andorians and Bolians, Green Skinned Space Babes from Orion, and orange Talaxians with polka dots. Most other races just have whatever colorations Earthlings have, since make-up isn't free. Thus, Vulcans can be black, white, or Asian. Klingons were played mostly by white actors in brown shoe polish in TOS, but black actors played Klingons more often as of TNG.
"Let That Be Your Last Battlefield", probably the most anvilicious episode of the original series, involved aliens who were chalk white on one side of their bodies and coal black on the other side. They were in a race war between those who were white on the right and black on the left, and those who were black on the right and white on the left.
For its part, the Star Wars Expanded Universe has a number of humanlike aliens and "near-humans" who are brightly colored. Most are explained as being normal humans in the far past who got separated onto different planets. Different living conditions and thousands of years' worth of microevolution resulted in people with blue and pink skin.
For instance, Twi'leks come in all colors of the rainbow.
The Doodlebops, a Canadian children's TV show. The cast are all brightly colored.
Farscape has quite a few technicolour aliens, with those in the main cast doubling as Technicolour Space Babes. There's priestess Zhaan, whose bright blue skin has a marble effect to it. This is particularly noticeable with her being bald. There's also Chiana, whose skin and hair are pale grey, with darker highlights in particular places - like her collarbone and cheekbones. Sikozu perhaps also counts, though her skin is mostly peachy-cream, there are scale-textured red-gold patches to match her bright red hair.
From "Rapper's Delight":
''... and I like to say hello to the black, to the white, the red and the brown, the purple and yellow ..."
In Hindu Mythology, some gods are often depicted with such skin tones. The most famous case is Vishnu, who's blue. Three of his avatars (Rama, Krishna, and Kalki) are also commonly depicted as having blue skin.
In Cirqus Voltaire, the Ringmaster has a bright green face, while some of the performers have uncharacteristically bright yellow and orange skin tones.
The various alien patrons in Big Bang Bar have blue, orange, yellow, and green-hued skin tones.
In Spectrum, most of the people featured have either light green skin or green-tinted skin tones.
Being inspired by pulp sci-fi, the Dungeons & Dragons setting Carcosa features people that come in green, red, blue, purple, yellow, black, brown, orange, transparent, and white, plus jale, dolm, and ulfire in a Shout-Out to A Voyage to Arcturus, and neither black nor brown is negroid, and white is not caucasoid.
Starting in second edition, a number of existing humanoid races became more colorful, such as giants and genies who could now be green or blue or what have you. Prior to this, their skin and hair color had just never been mentioned.
Warhammer 40,000 generally averts this trope with humans, except for the Salamanders, who have jet black skin due to how their recruiting world is sitting almost right next to their sun. This is more noticeable in the recent edition, as previous editions had them with vaguely African skin tones, while the new ones just slapped on actual black with little regard for highlights.
The Orks have green skin ("greenskin" is a common slang term for them) and the Tau have blue skin.
Tyranids, to a degree, also have this, mainly because they're biologically engineered. Still, one wonders why a hive mind would consider florescent pink with reflective metals to be good for camouflage.
The minor character Yoa in Beyond Good & Evil is blue. It's implied that she's "not a local," though she's still considered "human" to the game's scanner.
Bosco of the Telltale Sam & Max: Freelance Police games is "light purple", but has an African-American voice. His mother is a more typical "black" medium brown though.
Hugh Bliss, who is genetically Caucasian, can change his skin color to colors of the rainbow.
Guitar Hero World Tour's character creation mode allows the full spectrum of color to be used for hair, beard - and skin.
Nosgoth'svampires start off as pretty standard pale, bloodless looking folks, but as they get older they tend to display a large range of color, including bright green (Vorador), yellow-green (Kain), and purple-ish grey (Umah). Then there's Raziel, who while not having skin, has dark-blue muscle tissue for some reason. It's also worth noting that the original Vampire race had light blue skin.
The Sims 2. Every monstrous version of a sim has a different skin color. For example, alien hybrids are green, as are evil witches and plantsims (dark green and pale green with vines), vampires turn a shade pale, zombies become a greenish blue, werewolves are brown. Good witches don't change color, but apparently have glitter embedded into their skin for some reason.
Not to mention the endless mods you can download from the 'net which can give you just about any skin color you desire, up to and including rainbow.
The Sims 3 abolished the monsters (for now, anyway), but allows you to have exotic skintones right off the bat. In addition to normal skintones, there's also red, blue, and green. Plus, you can adjust it to any shade you wish. You can also set their hair or eye color to anything you wish and it will pass to their children. A man with blonde hair and a woman with black can have a child that has black hair with purple tips.
Many of the townspeople in the game Nox have fairly normal skin, but due to character customization, you can make the player character any color you want. Of course, no one notices if you happen to be a blue bald man walking around in your underwear...
In Yume Nikki, the Mall-like world is full of people of many different colors. The character Shitai, aka Dead-Guy-On-The-Pavement, has green skin. This is probably because he's dead and rotting, but a lot of fanart depicts him as a handsome man who just happens to be green.
City of Heroes allows you to create characters with skin in any of thirty shades spread across the rainbow or ten monochromatic shades from white to black in addition to a wide range of 'normal' skin shades. The NPC characters use this to a greater or lesser extent; for example, in the Outcasts NPC villain group, characters with ice powers have pale-blue skin, characters with fire powers have red skin, and characters with stone powers have grey-brown skin. The members of the Trolls NPC villain group all have skin that is a light green, a side effect of their use of the drug Superadine.
Geneforge. In the earlier games, only spellcasters had funny skin colors, but more recently, anyone could be blue, green, or hot pink.
Again, it doesn't really come up in idle chatter, and the protagonists' parents get turned into a dragon, so what does that mean?
The Beastmen of Morgal in Dark Dawn also tend to get pretty outrageous fur colors, especially since they're supposed to be... well, animal-people. The band alone contains a bubblegum-pink Cat Girl, a teal green fox, and a dark blue wolf. The king of Morgal is also blue-furred and has brown hair. Rather disconcerting. After the firing of the Apollo Lens, everyone left in Morgal apparently has gold fur now, bar Sveta who wasn't there during the firing.
Also in Dark Dawn, Blados of Tuaparang has blue-white skin. He was initially assumed by fans to be from Prox, but lacks the pointy ears and scales (and, you know, is from Tuaparang). Another character from his hometown looks entirely human aside from having Anime Hair and horns, so again, "not entirely human" might be the cause.
In a world where every car has a different paint job, the Putt-Putt series is bound to play this straight. It gets even better when you find you can change his color. It always starts out purple.
Pajama Sam has light blue skin, as with most of the other "normal" characters in the series.
In Jak and Daxter, the Sages' skin colors correspond with the type of eco they're the Sage of. So Samos Hagai, sage of green eco, has green skin, the Blue Sage is blue, and the Red Sage is, unsurprisingly, red.
In the Amiga and NES versions of Maniac Mansion, the Edison family all have cyan blue skin, while the rest of the human characters are "flesh" colored.
In Move or Die, Carla's skin is a strange bluish white color. She's probably supposed to be really pale from not being allowed outside.
Mass Effect'sasari range anywhere from light blue to dark purple, even green, in one case. Salarians run the gamut from red to green to gray to yellow. Krogan are a pale yellow, the hanar are a bio-luminescent pink, and the drell are seen in varying shades of green, blue, and yellow with red "gills". Suffice to say, it's a very colorful galaxy.
This is brought up by Shepard when Mordin Solus mentions how humans are the most genetically diverse species of all. Shepard points to all the different colors of other races. Solus brushes him off saying that physical appearance is only one factor in genetic diversity.
Canonically, there's Blanka's green skin in Street Fighter, as well as Oro's yellow, Necro's bleach white, Gil's blue and red and Seth's gray. While Dhalsim and Urien have more mundane dark skin colors, alternate color schemes like to give them all manner of strange, unnatural skin colors.
Akuma goes through this trope a lot. Canonically, he's a simple Dark-Skinned Redhead, though alternate color schemes will sometimes give him ashen gray or dark red colors. When he becomes Shin Akuma, his skin also sometimes turns dark red, and as Oni it becomes blue.
All characters from Monsterful. We have blue, gray, green, pure white, scaley reptilian, even textured skin and more. Justified, since they are all monsters living in a monster-only world.
The background characters in Supernormal Step are far more colorful than the main cast, and that's really saying something.
Zoophobia' has humanoid characters with pale green, white, blue and gray skin. And that's just the humanoid characters.
Schlock Mercenary has an engineered offshoot of humanity called "Purps", whose purple skin performs a type of photosysnthesis, greatly reducing their need to eat. And probably necessitating a change in police terminology.
Girl Genius: Agatha, Gil, and Tarvek change color every two panels in one of the arcs, due to a strange disease. Jägers can be any color from a "normal" human skin tone to green or purple, and some, like Mamma Gkika, change it at will.
Most of the cast from "Restaurante Macoatl'' come in multiple colors, but humans tend to come in the traditional browns and pink.
The Law of Purple: Caligulan natives sport a rainbow of random skin colors amongst their total population - it's a species trait. So far, this includes blue, green, red, white, pink, yellow, silver, purple, and more.
In the early days of Bloody Urban, only the vampires and other undead were shown with ridiculous skin colours, but since the switch from black and white to colour, there have been plenty of instances of this trope among the living as well. The most 'realistic' skin colours typically used in the comic are pure white with a pink outline, light olive green and brown.
I'm Not Mad started off with an Amazing Technicolor Population and then abandoned that after its second year (called season in the comic) reboot.
The gang of Blue Boys from Waterworks is composed of, you guessed it, four blue individuals. Except for Slick, who is only wearing a blue suit. (Curiously, we see two of the thugs in a flashback and they're white back then, like all other people in the comic.) The protagonist lampshades it at one point.
Connie: So, why are you guys all blue? Slick: THAT'S RACIST
One strip of NSFW fantasy comic Oglaf shows a Land of Indulgence where the population is this trope.
In Goblins, the goblins have multiple skin colors, even among the same clan (though there are hints that said clan is more cosmopolitan than most). This leads to the page quote.
Ctrl+Alt+Del occasionally has the player characters: One (blue), Two (red), Three (yellow) and Four (green).
MS Paint Adventures fancomic Superego gives each of the main characters a color, with both their physical appearance and their dialogue in that color.
Tower of God: Many races have peculiar colors, for instance the blueish-skinned race of Lurker or Anak who is green.
Justified in Olympus Overdrive. The gods' forms are dictated by the answers a contestant fills out on a questionnaire. Their favorite color is the color of the god's skin will be. The human partners all have normal skin tones.
Aliens as well as humans in Luminary Children have colorful skin, especially Koagi, who's green.
The Simpsons. They're yellow, and the trope applies only to characters that are supposed to be Caucasian or Asian. The show creators said this was so people who were channel-flipping would stop to see if it was something wrong with their TV. The "Caucasian" characters can be called either white or yellow. Meanwhile, Southwest Asians (Arabs and Indo-Aryans) tend to be rendered "white" (which is to say, "yellow") or "Mexican brown". South Asians such as Apu Nahasapeemapetilon and Southeast Asians such as the Thai restaurant owner will be "reddish-brown" (like Native Americans). Chinese characters tend to be "white" ("yellow"), while Japanese characters are depicted either as icy pale (as if they were all wearing geisha or kabuki makeup) or "white" ("yellow"). This is made even more confusing by the fact that the show's two most prominent Latino characters, Dr. Nick Riviera and Bumblebee Man, are yellow and brown, respectively.
Dr. Nick and the Bumblebee Man being both Latino and differently colored is Truth in Television, there's no such thing as a "Latino coloration".
Also lampshaded in an episode where Abe Simpson is considering marrying Marge's mother. Homer, concerned about he and Marge potentially becoming step-siblings, worries that their children will become freaks with "pink skin, no overbites and five fingers on each hand"...flash to a brief unsettling image of the Simpson children drawn as "normal" humans.
Krusty the Clown causes continuity errors with this trope. Depending on the episode, his unusually pale skin is either clown makeup or his natural color. However, that only seemed true in earlier seasons, and now it's implied to be due to Krusty's harsh, self-destructive lifestyle, with all his childhood flashbacks having him have normal skin.
There were a few times where normal colored characters appeared, albeit usually in a Lawyer-Friendly Cameo like the Archie gang. They did, however, have a legitimate Crossover with The Critic, where Jay Sherman was yellow.
Doug and his family were just about the only "flesh tone" people aside from Mr. Bone, Roger's cronies, and Mayor White—indeed, the most common skin tone in the Doug universe seemed to be purple. Interestingly, Doug's crush was a Dark-Skinned Blond.
For instance, Roger was green, Chalky was yellow, Bebe was purple, Mr. Dink was purple. Since Skeeter was blue (more like a dark teal, really), the prevalence of the Black Best Friend trope caused many to assume that blue is the equivalent of black in that world.
Judy:(Talking about Roger) Is he the blue one?
Doug: That's Skeeter!
This was explained by the creator in a bonus feature from The Movie's VHS release. When first drawing the main cast (as a child!) he often lacked flesh tone, and therefore substituted other common colors for other characters' skins.
Interestingly, this all suggests a kind of inherent caste system. Guardians are blue, the Matrices and probably other system-based sprites are green, and web-based sprites are orange. Viruses tend to be strange-looking in general.
In Voltron, the people from the evil planet (planet Doom in the English translation) are all different cool tones, including almost pure white, sky blue, deep cobalt blues, and even a green or brown earthtone from time to time.
Serendipitously, this was true not only for Golion (Lion Voltron), but Dairugger XV (Vehicle Voltron) as well.
Blue skin seems to be Japanese cultural shorthand for "alien". In America, aliens are either Little Green Men or The Greys; in Japan, they're tall blue dudes.
Cupido is set in a town with white (as in snow-colored), red, blue, and yellow people, who are divided into ghettos by an evil council. The titular character and his two friends are the only characters with realistic skin colors.
Not to mention Zig-Zag's minions (who are purple, pink, green, and gray), the purple-skinned One-Eyes, and the multi-colored populace of the Golden City. The desert-dwelling brigands, the witch, and King Nog all have relatively normal skin tones.
The Cobbler does turn brown immediately after leaving the city, though.
And Ron turns blue when he briefly goes evil in the episode "Bad Boy", with Drakken reverting to his original Caucasian tone (since it was Drakken's evil that was inadvertently transferred into Ron). In "Stop Team Go", though, he doesn't change color when zapped by the same device, since it's been modified by Electronique (herself an example of this trope, being light grey) to flip a person's moral polarity, instead of extracting their good and evil sides.
Many dark-skinned black people who have ashy skin can sometimes appear as being a light periwinkle, almost faded greyish-black in the most extreme cases. Considering that The Proud Family is a cartoon with rather colorful art direction, it could be inferred that this was one of the most blatant exaggerations for Artistic License.
The Fairly Oddparents' Francis the bully is gray. This is justified during an episode where Timmy wishes he wasn't born; in the alternate universe Jorgen shows him, Francis isn't a bully and is shown with tanned skin.
The gargoyles in Gargoyles have skin in just about any color. It's genetic, like hair or eye color.
The Children of Oberon (at least, the humanoid ones) run the color gamut, too. Puck is white (as in Caucasian), Oberon is light blue, and Titania is kind of green.
An episode of Fat Albert had the kids watch an episode of The Brown Hornet that dealt with a conflict between green and orange aliens.
Nobody seems to make much of it within the canon materials, but Gorillaz bassist Murdoc is green. Some early pictures depict him with what could be a regular olive skin tone, but he slowly went through yellowish-green to his current dark green. This might be something to do with his unhealthy lifestyle (drug and alcohol abuse and a long period of living next to a disease-and-zombie-infested landfill). Wild Mass Guessing has also suggested it might be a sign that he has demon blood.
Apparently, Murdoc has some serious problems with personal hygiene, but it's highly improbable that just this would make his skin so green.
In Making Fiends, everyone is a single unnatural color, not just the skin, but the hair, eyes, clothes, etc. are all one flat color. Most minor characters in the webtoons were grey or dull in shade, although the TV series makes them all more vivid. Lampshaded pretty much every episode as Vendetta always calls Charlotte"Stupid blue girl!".
Some of the background characters in The Problem Solverz have colorful skin. The town's several mayors have had yellow and red skin, and in one episode, the gang was freaked out by a teacher who was purple.
Half of the cast of My Little Pony Equestria Girls have skin that retains the color of their coat in pony form, presumably to avoid making the characters human ethnicities and opening a can of worms. (They almost avoided doing so, but many wished they'd taken the plunge, and the fact that pretty much everyone has had their color scheme significantly lightened has not gone unnoticed. But Not Too Purple?)
In Adventure Time, Finn and Susan Strong are the only humanoid characters with anything resembling a realistic skin tone. The Ice King is blue, Marceline is gray, Princess Bubblegum is bright pink, and all the other humanoid character (such as the bikini girls from "Shhh") have blatantly unrealistic skin colors.
The theme song of ToddWorld is titled "It's a Colorful World," and it certainly is. The main character, Todd, is blue, two of the other main characters are yellow, and another is green. This certainly extends to the wildlife as well— Todd's talking dog, Benny, is red, yellow, blue and green in various parts.
Ingesting certain silver-containing compounds causes argyria (silver poisoning, in short), the symptoms of which include one's skin turning blue. Certain other unhealthful conditions can cause red, yellow, or orange skin.
A particular enzyme deficiency can also cause blue skin. Read the Straight Dope on the Blue Fugates.
On a related note, prolonged contact with copper will turn your skin green. It's not a myth or something made up for that episode where the main characters get scammed on their class rings, it really happens and it's the primary reason why you won't see many copper ring bands, earring hooks, or anything else that stays tight to the skin.
Stan Jones, who unsuccessfully ran for Senate as a Libertarian, consumed home-made colloidal silver out of fear of Y2K problems, causing his skin to permanently become a blue-gray color.
Chrysiasis(gold poisoning) does the exact same thing as argyria where the skin turns blue-gray.
Eating nothing but carrots for an extended period of time will turn your skin orange, most obviously your palms and the bottoms of your feet. The effect will wear off once you change your diet.
This is because of beta-carotene, which is sometimes used as a yellow/orange food coloring, such as in the drink Sunny Delight (Sunny D). There have been reports of children turning orange because they drank Sunny Delight in excessive quantities.
In a fascinating and extremely rare genetic disorder, certain biracial children have been born with a "stripe" down the middle of their bodies (particularly their stomachs)- a dividing line between the dark and the light skin. Chimerism is more common in certain animals. Tortoiseshell cats have two lines of skin cells covering different parts of the body.
Some fake tan products don't quite get the color right and dye your skin orange instead.
A certain type of birthmark known as the Mongolian spot (warning: link contains picture of a baby's bottom) causes the skin around the lower back and buttocks in small children to appear blue. While most common amongst people of East Asian descent and Polynesians, it has been recorded in children across the ethnic spectrum.
Kids without "proper" flesh-toned crayons/pencils/markers/et cetera will frequently default to more colorful options. Oranges seem to be common.
Strawberry marks aren't all that uncommon in babies, but some are born with unusually large patches of bright red areas due to those. Rare cases have them covering half the face or more - this can be corrected with cosmetic surgery, usually. Can also occur with children afflicted with large areas of hemangiomas - some of the skin will have the large, bright red masses, but other areas are just flat and red. This is also often dealt with surgically, especially if the hemangiomas get too large.
The "Blue Fugates" of Kentucky have literal blue skin due to a genetic condition where they have high levels of methemoglobin. The father and four of the seven children he had with his normal-complexioned wife all have it, while the others do not. Besides them, the condition is very rare due to being a recessive gene.
If one ingests the element Gallium (or drinks it due to its melting point below body temperature) in extreme qualities they will turn blue. Specifically their blood will turn blue because Gallium will act as a substitute for iron in forming hemoglobin, the chemical that gives blood its color and caries Oxygen. Gallium hemoglobin works just as well as normal hemoglobin and we all have a little inside us naturally, except they are blue.
Even without genetic abnormalities or unusual diet, healthy human skin can be any shade of brown imaginable, and ranges from extremes of nearly white to blue-black. This is an amazing variety considering most of it only developed in the last 30,000 years or so of our evolution.