The Sue Colour Spectrum consists of colours which are impossible 1 in the normal world, but common amongst Sues. Sue colours are created when a Sue misspells a real colour; mistakenly merges two or more otherwise-innocent colours into a visual abomination; or modifies poor, abused colors with inappropriate descriptors. Suvian colors are notoriously eye-burning.
Suvian Colour Theory
Impossible to fully capture on film, this glose pencil case's true blinding quality can only be suggested by this image.
It is interesting to note that the real-life 'colour' magenta (halfway between purple and red) does not actually exist in the visible spectrum. In reality, purple and red are on opposite ends of the visible spectrum and this colour is produced when the human brain (and presumably, the brains of other sentient species) tries to interpret purple and red spectrum waves at the same time. It is fully an artifact of the brain rather than existing in physical reality. This may be the source of its obnoxiousness when super-saturated—and its usage as a more mundane stand-in for urple.
Urple may be reasonably interpreted to be 'more magenta than magenta itself'—a superimaginary beyond-purple colour unable to be fully fathomed outside of the mutable realities in fiction. How this could even be possible hints to the reality-warping powers of a Mary Sue: if the Suefic insists that a colour even more magenta than magenta exists, it is forced to... and may even be a normal mental interpretation of visible-yet-unfathomable badness in fic in the way the human brain creates magenta. If a Suefic insists that blello exists, wavelengths of blue and yellow are not allowed to be interpreted as normal in the brain, and instead are separated and processed as an imaginary, normally-impossible colour blello. Such unnatural colours are not able to be mentally interpreted in a realistic setting: urple paint must contain an amount of glitter to keep its hue outside of a Suefic, and bringing any of these colours into a Reality Room may dull them into normality unless the concentration of glitter is extremely high.
All Suvian colours are colour values that the minds of all known sentient beings in the PPC cannot normally process, and seeing them on a daily basis is stressing to sanity in an almost Lovecraftian sense. The high probability of running into urple and other Suvian, inconceivable colours likely contributes to the widespread madness among agents.
Documented Sue Colours
Antiblue
This most horrid colour is "the exact opposite of blue, but in the worst possible way." It is the colour of the uniforms (and of Aria the dragonling) at the Official Fanfiction University of Alagaësia.
Beep Blue
This bizarre colour was found by Agents July and Library in a Legend of Zelda fic. If you look at it, you start to hear beeping.
Bismange
This toxic combination of Pepto-Bismol pink and fluorescent orange is the school color of the Official Buffy and Angel Fanfiction University. Bismange was created when two students writing unlicensed crossovers in the computer lab opened simultaneous cross-continuum plotholes to Middle-earth and the Potterverse. Blasts of urple and wilver spewed from their computers and mingled, resulting in the disastrous new hue. Bismange has the power to dye anything it touches. It is near-impossible to remove from the skin and hair and completely impossible to remove from clothes.
Blarple
The unsightly combination of black and purple. One of the many colours discovered by Ari, Corolla, Nikki, Sergio and Tera in their second collaboration mission.
Ble
This sickly, drab shade of blello was encountered by Agents Dafydd, Neshomeh, and Alec on the mission to "Brown DragonRider of Pern," in which there were ble dragons.
Bled
Also known as 'purple's evil little sister', Bled is a combination of red and blue in a way that doesn't quite form purple. It causes migraines and especially affects people with mental disorders. The quickest way to get rid of Bled is through mashed turnip, preferably radioactive mashed turnips.
Bled is said to have originated at the International Academy of Hetalia Fanfiction in the summer prior to the school's opening. Two Staff Members are reported to have created it, but they are unavailable for comment. As of now, Bled's origins are unknown.
Bleen
A nasty combination of blue and green or black and green.
Blello
A disgusting combination of turquoise and yellow.
This was first documented in the Hogwarts Fanfiction Academy, along with wilver. Its first appearance was during the Canonquake in the first year, when the title of the fifth Harry Potter book was made known. After that, it became one of the colours of HFA. It was used during the fanwriter Quidditch matches as the colour of one team's uniform.
Blood Shot Red
A painful shade of red with the odd quality of shooting blood. This was found in an unknown Pokémon fanfiction (link unfortunately lost) and was quickly adopted by the Official Pokémon Fanfiction University.
Blunette
A nausea-inducing mix of blue and brunette, sometimes used to refer to the hair color of aqua-tressed characters. This was found in an unknown Pokémon fanfiction (link unfortunately lost) and was quickly adopted by the Official Pokémon Fanfiction University.
Buge
A mixture of beige and red (from the French rouge). It was discovered in this mission as a horrendous misspelling of Borg, and tends to act as a magnet for that particular species (as opposed to red in Star Trek, which acts as a magnet for trouble in general).
Crimsun
Described as "a disturbing mixture of hot pink, lime green, and orange." This is the signature colour of the Baker Street Fanfiction Academy.
Dark Black
Dark black was discovered by Nathan and Ellipsia in a Harry Potter badfic. It seems to be an eldritch shade of black.
Dark Grold
Glose's darker cousin, this colour is an unlikely combination of dark red and gold.
Eery
Originating from a misspelling of "eerie", this frightening color was first encountered by Falchion and Rashida during Act 2 of their first mission. It was described as "a disturbing, almost terrifying shade of red."
Gildver
A cousin of wilver, this color was created from a combination of gold, silver, and white. It was first discovered as an alicorn's coat color by Rayner and E.V.L. on their first mission.
Glite
Another cousin of wilver, this colour is an unlikely combination of gold and white. It was first discovered in the World of Warcraft fic "Reforged" by AnthonyD. As such, it has been adopted as the official colour of the Official Fanfiction University of Azeroth.
Glose
A sort of vibrant, blinding 'golden-rose'. This colour is common in Suvian-influenced sunsets.
Grack
A mind-bending color too dark to be gray, and yet too light to be black.
Greenk
Crimsun's less dangerous cousin, it lacks the orange component and uses less eye-aching tonalities of green and pink. This doesn't mean that the resulting colour is safe to see, though.
High Pink
High Pink was discovered by Aster, Lore, and Bendrick in a Dragon Age badfic, in which it was the color of a canon character's face. High pink itself is a pastel rose shade that, when looked at, smells like burning marijuana. Looking at it for too long, as the name suggests, produces a high.
Hreen
A downright confusing "hazel/green", the eye colour of a Discworld anti-Sue.
Hrown
This combination of hazel and brown was seen in the eye colour of a Character Replacement. It is less confusing than hreen, but only slightly so.
Lark Bled
Bled's even more mindbending cousin. This colour was created when a particularly annoying Sue apparently wasn't contented to only put together blue and red, and so she decided to put together light blue and dark red, adding another degree of impossibility to the colour.
Meen
A disturbing shade(s?) of green described in its original fic as being 'more greener'. This colour is a disgustingly dark shade of green under most circumstances; however, when it comes into contact with direct sunlight, it turns a bright lime-green. This colour was originally discovered in the fic "Joftrakloo Troll Shaman" by SugarRequired, and was quickly snapped up as OFUA's second school colour.
Pilver
A hideous combination of pink and silver. First documented in a Tales of Vesperia fic.
Plue
Pink and blue mixed in the worst possible way, also known as 'Bled's eviller little sister', and called Blink at the OFWho, where it is the school colour.
Purite Bledangle
When a Pokémon egg was being described as being both "pure white" and "with blue and red triangles", the resulting paradox created Purite Bledangle, which manages not only to be blindingly white along with being bled, but also manages to sound like a pseudo-scientific name.
This was found in an unknown Pokémon fanfiction (link unfortunately lost) and was quickly adopted by the Official Pokémon Fanfiction University.
Rolky-Mose
A vision-blurring creamy pink colour that makes all around it seem paler and fuzzier in comparison. It is a common skin colour for Sues and canon characters gettin' it on with Sues, where skin is usually described as 'milky rose'.
Smood Gred
The unlikely combination of smoke grey and blood red. Objects in this colour have a chance of emitting smoke with the same coppery smell of fresh blood.
Urple
Basically the ugliest possible mixture of pink and purple, capable of blinding unsuspecting people. Urple is one of the colours most commonly associated with badfic, especially Mary Sues.
Urple was first mentioned in Miss Cam's Official Fanfiction University of Middle-earth. In OFUM and other OFUs, urple is often used to torment unsuspecting students. There have been several incidents involving urple paint in OFUM, most notably the painting of Sauron and Morgoth's possessions, which led to the short-lived Great Morgoth/Sauron Alliance. This deed, and several others, were committed by two mysterious figures known as the Urple Bandits. The identity of these two has never been confirmed openly, but they are widely believed to be Merry and Pippin. Urple was also revealed to be the color of the obscure sixth Wizard Ragna the Urple, who had overslept and missed the boat to Middle-earth by a few millennia (much to the delight of the other five, who never really liked him).
Uburple
This super-saturated urple shade is found only in the worst of the worst of prose, and is so urple it surpasses the capabilities of normal vision and comprehension to process it. It is known to invoke extreme revulsion and frustration to the point of madness. As ultraviolet is to violet in the visible, conventional wave spectrum, uburple is to urple.
The Eye of Argon is notable for visible uburple in a formally published work.
Whirple
A horrifying combination of white and purple. First documented in a Tales of Vesperia fic.
Wilver
This is described as the ugliest possible combination of white and silver. Wilver was created at the Hogwarts Fanfiction Academy.
Real Life Sue Colours
ATC - I'm In Heaven When You Kiss Me
If you're especially masochistic or have been taken hostage by your morbid curiosity, you may see many of these Sue colours and more in the music video for ATC's "I'm In Heaven" (right). Glopsnerch and sunglasses are suggested before viewing.
This video consists of various Mary Sues, Marty Stus, and several Cute Animal Friends frolicking in a Sue-world to very irritating music.
From timecode 2:46 onward it also contains an example of what Suvian telepathically-enhanced singing sounds like. The effect is considerably dulled in a recording, but it gives you an idea of why you Do Not Want to hear it for real.
Also, tetrachromats can see more colours than other people can.
1 The above video proves this wrong. Very wrong.