Personally with 4 players, I like to see all 4 joysticks at the same color (usually black) and just have the buttons different. As for the button colors for each player, I like blue, red, green, and orange.
Try out some CP designer programs to test your colors out. Look at A TON of examples before committing to any colors as well.
EDIT: I think that the aluminum joysticks look great as well if you don't mind the extra price.