When I waited tables a few years ago, my experience was the same as yours; the majority of the black patrons left crappy tips. After a while, my coworkers and I started referring to tips left by black patrons as the STD (standard two dollars) because they always seemed to leave $2 no matter how large the bill was or how many people were in their party, and this was at a restaurant where the average price for a meal was $15-$20 per person.
One time a black man and his girlfriend came in and ran up a $212 bill, which included a $175 bottle of Dom Perignon. He handed me a stack of twenties and told me to keep the change. I figured it was probably $240, which would have been nice for me, but when I counted it, it turned out to be only $220...a freakin' $8 tip on a $212 check. What a lot of people don't know is that waiters usually have to pay a certain percentage of their total food and drink sales to a pool for busboys, hostesses, etc. At the restaurant I worked at, it was 3.5%. Since 3.5% of $212 is roughly $8, I essentially made no money for serving him. Any less than $8, and I would have actually lost money.
I found that Europeans didn't tip well either. In fact, sometimes they didn't tip at all. I asked my friend who has family in Europe and she said it was probably because over there people don't tip, either because waiters actually get paid decent wages or maybe just because of the culture difference, so when they come to the U.S., they're just not accustomed to it.
Edit:
Hey CT2TXtech, I just noticed that you work at Pappadeaux. That's where I worked (in Houston).