Pick any color spray paint you like when you're at Home Depot or Walmart... I like "aluminum" for brakes. Grab a can or 2 of semi gloss black while you're at it. Next time you happen to have the wheels off, crack a beer or whatever you like to drink. It's best to do this after a good pressure washing, by the way. Spray the calipers or drums generously with brake cleaner. Mask off anything you don't want paint on if you're feeling professional. Alternatively, you can just stick pieces of cardboard in there blocking the spray. Paint the brake components in multiple light coats. Then, take the semi gloss black and spray around inside the wheelwells and visible components. It makes a big difference. Regular spray paint actually holds up well in my experience. Maybe not if you autocross your car or something, but just fine in SoCal traffic.