Ok, I am slightly changing my mind about different colored buttons. I just finished up the control panel for "The Return of the Neldog" (Neo Geo layout, christmas gift for someone), and I used 4 different color buttons (A,B,C,D each a different color), along with purple start buttons (a 5th color), and black joysticks (a 6th color), on a sort of glossy rubber overlay and it looks awesome, kind of like someone spilled a bag of skittles.
I'll photograph it today and then post it when I come back to work.