Black Japan Paint is basically a formulation of black paint that originated in Japan, It had advantages over other formulas such as very good adhesion to metals, toughness, flexibility, and faster drying.

One of its main ingredients was bitumen. This accounted for much of the toughness and opaque black color- but it also meant there could not be red or blue japan paint.

Ford used it on their early vehicles, until the introduction of nitrocellulose lacquers, which allowed for more color choices.