Abstract: A process for forming a coating on a metal substrate includes contacting the substrate with a molybdate solution having a pH of between 3.5 and 5 inclusive containing an acid with the proviso that the acid is not nitric acid. The substrate is contacted with the solution at a temperature between 30 and 75 degrees Celsius and results in a yellow coating that is kinetically stable from 20 seconds to 300 seconds before the coating darkens to a final black coloration. Water washing of the yellow coating precludes further color development. The resulting yellow coating is amenable to overlayering with a seal coat.