In my premed pre-reqs, no. We made up around ~10% of each class but for my graduating class, that percentage dropped a bit over the years.
In my upper-level science courses (Chemistry major), yes. I was often the only URM and the one of few females in predominately male ORM classes. For the most part I was okay however I definitely felt the need to prove myself almost constantly though. At times it seemed like other students would not take me or my input seriously until they saw my grades. Once they saw I was on par or higher than them then it felt like I could finally join the 'team'. Additionally, aside from my peers, I felt I stuck out like a sore thumb to my professors. (I even had an experience where I went to walk-in office hours for a professor of a 400 student O Chem class and he knew my name before my ever saying so.) I felt like this pressured me to do what I could to outperform my peers so I would not be looked at as the underperforming minority who did not belong.
Outside of classes, I was the only URM in some of my EC's as well. Same story pretty much. I just had to fight the stereotype that URMs always perform worse than their peers and that all black females have a ghetto, loud, and angry side to them (couldn't be further from the truth).
My experiences have been both positive and negative in a sense. Negative for what I said above and positive because they have prepared me for the future. I chose my undergraduate institution for this very reason. I knew by pursuing medicine I would be in a similar environment as a minority and wanted to the opportunity to adapt to the environment before medical school. I think it was also positive in the sense that I got the chance to educate some of my peers had never been around many URMs until college.