How to deal with racial insensitivity in an academic environment? I am an undergraduate research assistant in a biology lab. I was having an informal conversation while working at lab with my professor and a colleague of him. In the middle of our conversation, my professor passed a racially insensitive remark at me (I can reproduce here if someone wants to know). However, he realized it and walked away immediately. I am very upset. 

But after few hours, he came back and he was conversing with me like nothing happened, but I am still upset. Can you all tell me how to handle this? My options are to ask him if he did that unknowingly or to keep quiet. But I really want to know if he feels sorry for what he said. I really don't want to complain to his superiors, but I want him to apologize to me for what he said. Is this unreasonable? if not, how should I go about dealing with this person?
In your question, However, he realized it and walked away immediately. and But after few hours, he came back and he was conversing with me like nothing happened

indicate to me that he felt sorry and didn't know exactly how to deal with it.

Professors are also human. They make the same mistakes others do.

I would suggest you to talk to him in person about this incident politely and seriously. Tell him that you are upset with the remarks he made earlier and explain to him why. Don't be emotional.

Whether or not he will apologize is up to him. If he doesn't offer apology to you after you talk to him, then talk to his superiors if you want the apology.