Don't judge someone by his color.
Stand up for it!
We are all equal and we shouldn't let a prejudgement destroy that fact.
Racism is a shame for all the human beings and we should stop it, it's not fair that everyone looks angry when a black man is walking on the streets, they should act the same to that person as if they would see a chinese or an eskimo.
So if you ever excluded someone with another color then you just because of that reason, do something about apologize and try it again.
It's not that hard, and it will only give you new friends!