The Neathbow

"A book for children. One page is devoted to each of the colours of the Neath, which are not found on the Surface."

The Neathbow is the collective term for seven colors which cannot be seen on the Surface. They are most commonly observed in the Neath (hence the name), but they also turn up in places like Parabola and the High Wilderness. The seven colors of the Neathbow are irrigo, violant, cosmogone, peligin, apocyan, viric, and gant.

Origins

The Neathbow was likely inspired by real-life impossible colors. The shades of the Neathbow are likely inspired by the additive (used for light) and subtractive (used for pigments) color wheels. Below are fanarts of the Neathbow arranged to correspond with those color wheels:

• 
  Additive. Art by MidnightVoyager
• 
  Subtractive. Art by MidnightVoyager

Each color's name likely has the following inspiration:

• "Irrigo" is a Latin word meaning to flood or overwhelm, or to diffuse or shed
• "Violant" may stem from "violent" and "violet"
• "Cosmogone" stems from "cosmogony", the study of the origins of the solar system, and "cosmos" and "gone"
• "Peligin" is seemingly a portmanteau of the Latin pelagus, meaning "sea," and the color fuligin. Fuligin, in turn, is darker than black, and is derived from the English word "fuliginous" meaning soot-like; this color was used by Gene Wolfe in his science fiction novel The Shadow of the Torturer.
• "Apocyan" presumably derives from the color cyan, which has a similar hue, and the Greek prefix apo-, meaning something between "off, away" and "descended from" - like the words "apostate" (gone-away-from-a-cause) or "apocalypse" (un-covering).
• "Viric" probably comes from the Latin viridis, meaning "green, blooming, vigorous," a word that also spawned the name of the similar color viridian.