The old pre-crazy Harvey would have been green all the way, but then there *is* the argument that it takes an assload of willpower to keep Big Bad Harv at bay. But that's assuming that he *is* keeping Big Bad Harv at bay, and rather isn't trapped in a stalemate deadlock that keeps either one of them from overpowering the other, because they're both equally half of a human being?
And post-crazy, isn't willpower exactly what Harvey lacks, thus relying on the coin? At that point, all he has left to fight the bad side with is hope that he'll get better and triumph, is it not?
More practically speaking, I'd think Blue and Red would be a better color scheme, whereas Green and Red might result in "Christmas Lantern Two-Face"...