Before revision: Philip K. Dick's 1969 novel Galactic Pot-Healer mentions a color "rej", Terry Pratchett in his Discworld series that began with The Colour of Magic (1983) describes "octarine", a color that can be seen only by magicians and cats; and Marion Zimmer Bradley in her novel The Colors of Space (1963) mentions "the eighth color" made visible during the FTL travel.
After revision: Marion Zimmer Bradley in her novel The Colors of Space (1963) mentions "the eighth color" made visible during the FTL travel.