Teaching your children to be bias

Once again, I am at my wits' end with my ex...for a number of reasons but the last straw was him trying to push his racist views onto our children. Him and his girlfriend both have the same opinions on how races should not be mixed, that we all belong with our own kind and that interracial relationships are just not right. Mind you they blatantly told my 10 year old son this. How do I approach this with my ex? I already know the answer. I don't. Why? Because he is never in the wrong. He had no regard to even throw the "n" word around our son. I am thoroughly disgusted by this. My son came to me upset, trying to understand why his Father is like this. I have raised my children to accept people of all colors and they have friends of many races. I am really at a loss on this one. But my children know that yes, people have a right to their own opinion, but not to try and impose those opinions into facts. I can no longer allow my children to be exposed to this type of behavior, among many other reasons...