Going through my dad's collection music, there's tons of white guys/all white groups from Iron Maiden and Ozzy to Metallica and Poison. I was curious why there weren't many black people in this specific genre, I don't think it was because people like Bruce Dickinson refused to play with a black guitarist or anything but it seems on average there'd be at least a few black guys scattered in here or there. I could be wrong but I don't think there was the same stigma against black musicians in the 80s as there was in 1956, so why didn't it happen?
Ooh, boy, do we have some answers for you. There's always another angle of approach that somebody could write from, and I don't want to discourage any more unique takes, but between this answer by u/hillsonghoods and this answer by u/texum, I think most of the bases are covered.