Just painted mine red but its a silver car. However, red would look good on a black car. The paint came from Halfords and very pleased with the result but after a few decent runs is looking a bit dusty.
I'm starting to think about doing mine - shortlist was red (but emphasises the smallness of the callipers), so now on a shorter list of silver or black. Will probably go for black and do the Zed and the Discovery from one pot of paint.
I rebuilt a set of 330I calipers, stripped them to bare metal, etch primed and sprayed them with silver grey smoothrite, just remember it's not brake fluid proof!