Colors that don't exist

Fuligin ("darker than black," the color of a torturer's cloak)
Octarine ("the color of magic," a flourescent "greenish-yellow purple")
The eighth ray (used for propulsion on Mars)
The colour out of space (almost certainly described as "squamous")
Infra-green (used to find the mushroom planet)

Grue and Bleen ("grue ... applies to all things examined before t just in case they are green but to other things just in case they are blue")

Hooloovoo ("a superintelligent shade of blue" probably not on the spectrum from Ultra-violent to Infra-dead)