Red, Yellow, Green, and Blue colors are
the most common colors
Which are available in the rainbow treehouse sets with black. (and with three sets he can start with an all-yellow set for himself if playing martian chess). And as was mentioned before, it's a lot easier to play/make other games with multiple colors.
As for boards, I've got a feeling it may be cheaper/easier to have ee0r's acrylic boards professionally produced/cut than for him to cut them in his basement/garage or wherever he does such madness; but I haven't been able to discuss it with him.
Also, a red/black checkerboard would look fairly mars-ish in my opinion. There were rumors and plans for a martian chess set a while back, but I think the project was dropped when they moved to the treehouse distribution method (along with all the other boxed sets).