I want to know why Luke has a golden lightsaber on the Shadows of the Empire novel cover.
Probably the same reason everything else is yellow. I mean even Vader looks kind of yellow. The yellow colour scheme in general seems to have to do with the sun behind the SW logo, it kinda looks like a moon, but this novel does revolve around the Black Sun organization so it might have something to do with that.
Also Struzan has switched up the colours before for the sake of symbolism, such as the reversed saber colours of Luke and Vader on the Revenge of the Jedi poster, which he even claims was done subconsciously.
So it’s probably just an artistic choice.