That is a very interesting question, minimus, and I'm sure you understand that the answers will vary according to location, experience and outlook of the person answering.
The first two congregations I associated with were in the Alabma cities of Tuscaloosa and Birmingham respectively. In both congregations, the overwhelming majority of publishers were black. The white Witnesses felt welcomed there and got along famously with everyone else. So I never saw any racial tensions there.
Then I moved from Alabama to Colorado where I spent the next 30+ years. For 23 of them I was an active Witness in two congregations there. Blacks made up less than 2% of the population in Boulder, the city I lived in and that was also reflected in the congregations I was a part of. Still, up until the time I was disfellowshipped, I can say that I was always respected and treated well. That was true as a whole for my entire stay in Colorado. Maybe my experience was atypical, but I can honestly say I had few problems with racism as a Witness.
I'm now back in Alabama caring for my aged mother and have nothing to do with either the WTS or Jehovah's Witnesses now. The racial climate in Alabama has changed for the better in the years since I have been away. That change may well be reflected in the congregations here now, but I can't speak to that of my own knowledge. Previously, Witnesses did better as a whole with the race question than non-Witnesses but with everything being less troublesome now, that difference may no longer be as marked or even exist nowadays.
Quendi