When racist grandparents misbehave?

[oatmeal55]

My mom and I took the day off and took my grandparents out for lunch. My grandparents are very old (90), very italian, and a bit senile. They like Olive Garden but the one in their neighborhood has a lot of black employees so they didn't want to go there. Instead, we went to another italian restaurant (still a chain but more upscale). Our server was half white half black. He was a great server and our meals were really good. Aparently though my grandfather thought he was italian. After our meals, he decided to tell the server how he was happy he didn't get a black server and how he was a "good" italian guy. Then my grandmother scolded my grandfather and said "well you don't know he's italian, he might be greek". My mom and I were horified. Our server was very uncomfortable, but could tell my grandparents were just old and brought up that way and he played along and took it very well. We left him a huge (50%) tip and apologized profusely after we had gotten my grandparents into the car. We still feel bad though, the poor guy did such a good job yet had to endure racist bashing. Is there anything else my mom and I should have done or still could do to make it up to him? Or should we just leave him be, and maybe not go back anytime soon?
I just want to add that my mom and I are not the least bit racist and couldn't care less if our server was black, white, asian, italian, or whatever. But my grandparents are very stuck in their ways or growing up in the early 1900's.