I don't think people are actually denied admission on the basis of race any more, but there is a lot of self-segregation in the States, a lot of venues where management, entertainment, and customers are either all-white or all-black.

My own experiences as the only white person at a predimnantly-black club, or one of a small group, have always been perfectly cordial. Of course, New Orleans isn't representative of anyplace else in the US (or in the world, for that matter).

To summarize what I've concluded on the main subject here:

~Blacks in the US created a folk culture of their own, rooted in the shared experience of being taken straight from Africa, in large numbers, to the plantation South.

~Blacks arrived in Britain in much smaller numbers, usually by way of the Western Hemisphere rather than directly from Africa. What musical and cultural influences they brought with them was already the product of some interaction with "western"/white culture. While individual musicians of African ancestry undoubtedly made significant unsung contributions, I would say that whatever impact they made, they made as individuals -- not as representatives of a distinct ethnic subculture with a life of its own.