Now that I think about it, the PetSafe Small Dog Collar is made of a black soft-touch rubber collar with a molded base for the receiver, but the top piece of the receiver is translucent smoke gray -- so the LEDs (red/green) can shine through.
I would stay clear (pardon the pun) of white. After some consideration trying to keep it clean would be a pain. (oops another pun). The clear, dark gray, or black in that order would be my preference.