Black people are notorious for not tipping and everyone knows it.
No doubt, there's some truth to that, but it's certainly not universal and it's getting better (according to my friends in the industry). Also depends upon the restaurant.
Is tipping primarily a learned behavior?
For the most part, but there are individual variations. I don't understand people who are hesitant to tip generously. I tip the hell out of bartenders, and, believe me, it pays off in the long run. I also tip well for food service. I just think it's part of the bargain. It's a tough job and I appreciate the work they do. If the service sucks, and it's actually the server's fault and not that of the kitchen, etc., the tip will go down accordingly.