I remember in one rockumentary or another hearing the account of how Elvis cut "That's Alright" and it got played on a local Memphis station for a couple of days. Then the radio station had him in studio to talk for a minute or two, and he was kind of mumbling, and one of the few things that people listening could really understand was when he said what high school he'd just graduated from. And apparently this was well-known to be a predominantly black school & so a lot of folks assumed he was black.