Any AutoZone or equiv. will carry a Duplicolor kit in a few basic colors for~ $16. If you go to Duplicolor's website, there are videos for technique.

http://www.duplicolor.com/products/caliper.html

Or, as was stated, any high-temp enamel can be used and there are more colors available.

If you want to use a rattle can, be prepared to cover the WHOLE CAR with a tarp, and tape off anything you don't want overspray to ruin. This includes the rotors and the wheels and tires sitting 3 feet away!

I used CRC Brake cleaner and a couple of old toothbrushes to cleanthe calipers before I started. If you are working over a painted floor, the brake cleaner will make a heckuva' mess. Use a dropcloth there too.

Good luck!