If they add the tip, that's what they get, not one penny more. I usually tip 20%. If the service is exceptionally good, I'll add a little more. If the service is exceptionally bad, I'll speak to the management. Servers with georjec2's beliefs regarding black people usually do a half-a $ $ job of serving, and I tip them accordingly. I'm not going to reward mediocre service just to try to dispel a stereotype.
And I don't blame you. Too bad there aren't more of us like you willing to tip according to the service given.