Male or female, gay or straight, black or white, all subs know that all they have to do is submit, do as they are told without complaint, and understand that they exist only for their owner's pleasure. Simple, really.
Yes there is but most of us who are turned on by it like the huge shiny black cocks love seeing our white wives with huge BBC. Probably because it's still like a taboo mind thing. Also many of the couples out there seek out black bulls as well so that's what's filmed. Me personally id rather see my wife with a strong powerful black man with a huge dick vs some avg white guy like myself!