I have to admit I'm quite unsure of the details of his shifting abilities, not just about the colors, but also about his ability to form details. Mostly I've gone with what I thought looked best/coolest to me (which I assume is in the best tradition of creating brain-breaking comic continuity, so why shouldn't that approach do for fanart as well? *g*). Anyway, I've seen at least panels where his orange and violet colors blend into each other at least, so I figured that if he creates other colors there might be bleedover as well.