The exterior decoration of railway rolling stock is called livery. Over the course of its history, the SNCF has used many different liveries, depending on fashions and changes in equipment. The first liveries were black, then after 1938, they became dark green with a yellow stripe, for electric and diesel engines. Some of the more prestigious models were given light green or blue metallic colours. Other liveries were then assigned according to the line, in order to differentiate them. They may also vary according to the design of the locomotive.