it's just interesting to me that the first thing you did was try to point out that some black people are prejudiced too, as though to justify white people being prejudiced. which sadly falls perfectly into lockstep with some of the other sentiments you've expressed in other threads.
it would do you well to study the correlation between race and socio-economic status. yes, black people tend to tip less, just like - shockingly - people at the bottom rung of the socio-economic scale tend to tip less. you do the math.
As someone who both served and bartended, I can say blacks definitely tip considerably lower that other groups no matter what kind of service is provided.
I never discriminated based on the color of people's skin however I let the way they conducted themselves towards me decide the service they would get, to me even worse than the non tipping factor is the vast majority of blacks would be disrespectful obnoxious and rude compared to other groups, I could always deal with a low tip if I knew that they probably needed the money more than I do.
There are always exceptions as in anything there were several regulars who were respectful and tipped well, but I would say at least 80% tip poorly and at least 60% were rude and disrespectful reguardless of the level of service.