I like using a coat (going rattle can) bast black over the outer surfaces, over coated with interior Dark Charcoal metallic or a thin coat of Zinc Phosphate rattle paint just to darken the look from cast to hardened.
Then sand the machined surfaces, then a satin clear coat. Remember to keep all coat very light as you don't want to give the look of being painted and loose the surface details. Of course the paints can may be an issue (just guessing) if you drive the car allot and really get the brakes very hot.
