Colors such as imaginary and chimerical colors that do not appear in ordinary visual functioning. Different color theories suggest different hypothetical colors that humans are incapable of seeing for one reason or another, and made-up colors are routinely created in popular culture. While some such colors have no basis in reality, phenomena such as cone cell fatigue enable colors to be perceived in certain circumstances that would not be otherwise.
An imaginary color is a point in a color space that corresponds to combinations of cone cell responses in one eye that cannot be produced by the eye in normal circumstances seeing any possible light spectrum. No physical object can have an imaginary color.
A chimerical color is an imaginary color that can be seen temporarily by looking steadily at a strong color until some of the cone cells become fatigued, temporarily changing their color sensitivities, and then looking at a markedly different color.
Some works of fiction have mentioned fictional colors outside of the normal human visual spectrum that have not been observed yet, and whose observation may require advanced technology, different physics or magic. Introduction of a new color is often an allegory intending to deliver additional information to the reader. Such colors are primarily discussed in literary works, as they are obviously impossible to visualize (when a new color is shown in the episode “Reincarnation” of the animated show Futurama, the animation for that fragment of the show is purposely kept in shades of gray).
One of the earliest examples of fictional colors comes from the classic science fiction novel from 1920, A Voyage to Arcturus by David Lindsay, which mentions two new primary colors, “ulfire” and “jale”. The Colour Out of Space, a 1927 story by H.P. Lovecraft, is named after an otherwise unnamed color, usually not observable by humans, generated by alien entities. Philip K. Dick’s 1969 novel Galactic Pot-Healer mentions a color “rej”, Terry Pratchett in his Discworld series that begun with The Colour of Magic (1983) describes “octarine”, a color that can be only seen by magicians; and Marion Zimmer Bradley in her novel The Colors of Space (1963) mentions “the eighth color” made visible during the FTL travel. “Plueragloss” is the favorite color of a character who is a natural inhabitant of the afterlife in the television show The Good Place. In the show, plueragloss is described as “the color of when a soldier comes home from war and sees his dog for the first time.”