Black or gray top ply.
Seriously, anything else makes your board look like shit after one session once your grip starts getting messed up.
The only color I refuse to skate, however, is that baby diarrhea green that so many decks have. Fuck that.
For the bottom ply, anything that is in contrast with the graphic, so everyone will see the marks and notice how balanced your nose slides are and get super stoked on you as a person.