The plenums are aluminum for heat disipation reasons. The paint on the outer skin of the plenum would take heat from both sides. I would recommend either a caliper paint like Audioquest states or go with powdercoat. Other than that there is Swain coating as well, which is of course all function. If you want "the pretty", then chrome or nickel plating are options. I personally like the powdercoated plenums myself.