Herb Jeffries is best known for his monster hit song "Flamingo" from 1941, but from 1937-9 he made several low-budget Westerns aimed at Black audiences. Yes, he was a "singing cowboy" when Roy Rogers was still Leonard Sly.

In Herb Jeffries' movies both the good guys and the bad guys were Black.

He also qualifies as a TV Western cowboy (well, sorta) (ex Wiki):

             "Jeffries went on to make other films, starring in the title film role of Calypso Joe co-starring Angie Dickinson in Calypso Joe (1957). In 1968, Jeffries appeared in the long-running western TV series The Virginian playing a gunslinger who intimidated the town. In the 1970s he appeared on episodes of I Dream of Jeannie and Hawaii Five-0. He later directed and produced Mundo Depravados, a cult film starring his wife, Tempest Storm."