well, you could always make one that uses most of the rainbow.. after all, their visual reception might differ from ours. but, for example in Eve online.. let's say, Caldari race.. their ships in general are metallic gray or metallic blue, and something between those two.. their exhaust glow bright blue, as do their nav lights. then there's minmatar. their ships are usually rusty, corroded looking, and their exhaust glows yellow, and in this case their nav lights are orange. you get the idea, right?