Ever wondered why car radiators are black? It helps to radiate the internal heat away faster. So a black car should radiate away heat at its painted surfaces more efficiently. Conversely, a white or shiny surface might be better at reflecting the sun's hot rays on the same surfaces to keep the heat away in the first place. But most of the heat accumulating in the car to affect any electronics comes in amplified via the glass windows, not painted bodywork. So, enjoy that stone black without worry - just remember to place a shade of some reflective material against the hot sun at that huge windshield glass.