Sometimes it is not racism just disappointment as if you are being held up to a different standard. For example when I volunteered in the ER, a man asked me why I was volunteering. I told him because of my interest in medicine etc. He then said, "oh you are not doing this for a program or some kind of probation/court ordered community service?" I told him no. He then shook his head as if to say "okay, not bad... good for you".
Or in other situations when volunteering, patients/families would ask what I did. And when I told them I was a college student their eyes would perk up and they would say "oh that is great". It wasn't a bad thing they would always be so happy for me. In some places, for blacks that type success is unexpected. And in other places it is not welcomed.