Nothing could be more wrong.
Black CowboysIt is an unfamiliar part of the history of the old wild west to most, but there were actually about 10,000 to 15,000 black cowboys in the late 1860's and onwards. These men actually held quite a significant place in this part of history, after the Civil War, many of the freed slaves moved west to make a new life.
They worked on ranches and in cattle drives, and also rode in the many rodeos. Some of them joined the cavalry where they were known as Buffalo Soldiers and they brought back much needed meat and hides to resupply many of the stores.
A black man with a gun would have brought every white Texan for miles to the lynching party.
It's pretty funny that you think it's some new thing for westerns to be wildly beyond historical reality too.