black or brass

There is truth to the color's relation to dissipation of heat but that rule is not limited to only black. Paint companies have used additives in any color paint to dissipate heat. Ceramic is the most common and works well. Most brake caliper paint is ceramic.

Read this:
http://www.offroaders.com/tech/paint-it-black.htm

Black radiates heat in the infra-red spectrum better than other colors, which tend to "specialize" by radiating less efficiently in the infra-red and more in just their color portion of the spectrum.

Speakers analogy: With regard to black being able to radiate heat well, heat is like a bass note, black is a woofer, and other colors are "mere" tweeters.