Well, you can either treat this as "racism" as in: "you grew up in multicultural surroundings but you're still a racist" or "racism" as in: "you grew up in communist China where you never even met a white person".

If you think those are both the same things then not sure what else to tell you.

And yeah, OP needs to talk to them. Not because of him or the family but because of the gf. If things go south he can be like "i tried", but for some reason the girlfriend thinks that would change things so might as well give it a shot. It would be awesome if suddenly everyone would get along, but until then yeah you should at least try to make things better.