My two cents on your question:
Kids didn’t care if it was white or black music, but ‘race records’ were not played on top 40 and not sold outside the black areas or big cities.
DJ Alan Freed is, correctly in my opinion, credited with discovering that race or black music would sell to white audiences, which started the crossover.
The Rolling Stones copied black tunes right at the time of the “British Invasion” or the British fad in America. This resulted in white rock and roll becoming the phenomenon rather than black R&B/blues getting the ride.
I wish I could remember the song that, to me, sums it up. There was an incredible song released by a black group, immediately covered by a brit group. The British song soared.
I don’t really think it was a black/white thing, well other than there were a lot more white teens buying records and they gravitated toward white groups. I think it’s kinda understandable that white teens would like jagger more than james brown.
But, IMHO, at the beginning, the brits stole the black music and did it more poorly than the blacks.
As for the “white bread Mainstream America” bit: in my part of America, the South, it wasn’t a black white thing, but was a generational thing. Parents, in general, hated it, kids loved it.
FWIW.
(Elvis of course is a whole ‘nuther story line.)
That dog won't hunt. Everybody copies everybody else. White musicians no more "stole" black music than black musicians stole white music because black musicians used non-African instruments like pianos etc. to make their music. Everybody is influenced by everybody else. Did Charlie Pride steal c&w? If I claim credit for writing a song I didn't write, then yes, I stole that music. But if I make a cover of song, I didn't steal it, I just made a different recording.