I inferred that was what you meant, but I wanted to be certain.
Yes, there is a stereotype that blacks are bad tippers. Yes, there is a stereotype that black women are the worst tippers and more demanding as diners.
It goes beyond a stereotype, I guess, because there are multiple studies that show blacks tip less than whites (including studies done at Cornell, which has the nation's finest academic programs in hotel and restaurant management).
On the other hand, I know from black friends and friends who have worked as servers that the problem frequently has circular causation. Servers may expect to receive a poor tip from a black diner and therefore don't offer the same quality of service that they offer to other diners.
Blacks are sometimes faced with a dilemma: do they tip poorly to reflect the poor service they received, thereby perpetuating the myth that blacks are poor tippers - or do they try to break the stereotype by overtipping for the quality of service received. Or do they take the time to explain the whole thing to a manager and server?
Then look at it from the server's viewpoint. Are you going to go out of your way to provide extra service if you know from past experience that a black diner (or a senior citizen diner - also bad tippers - or a teenage diner - also bad tippers) is likely to give you a bad tip?