Racist Sibling

My SO is a great man and my family loves him with one exception, my oldest brother.  He is racist and no one in the family can explain why or how he became that way.  He does have a different mom than the rest of us, but he didn't have much to do with her growing up, so I'm not sure if he could have gotten ideas from the rest of his "other family."  He does have black fishing buddies, but they share his belief that races should not mix.  My brother has never even met my SO.  He has met my son and has been very kind to him.  He plays with my son and treats him just like the rest of his nieces and nephews. I feel that he is kind to my son because my son is very light and its not readily apparent to most people that he is half black, so he is chooses to ignore it.  My oldest brother has never acknowledged that my son is mixed, or that I even have a SO.  He doesn't ask questions about him or invite him to family events.  I don't want to write my brother off, but this situation is very straining on our relationship.   I would like to visit him as a whole family unit, not just my son and I.  It would also be wonderful to have the entire family be able to visit together at our parent's house.  My other siblings and parents don't know what to do about our brother.  They love him and me.  My SO's family is amazing to me.  All of his siblings are treat me so well.  His mom loves me and our son.  This just makes me feel all the more guilty that my brother doesn't even acknowledge his existence.  This has gone on so many years I don't know what to do about it.  The other thing is that I think that they would get along great.  They have a lot in common.  They both like a lot of the same music, both grew up hunting and camping... Any thoughts?