Poor you, with a father like that.
Re not knowing what to say about your sons' marraiges, I'm afraid I wouldn't say anything either. What's to say, other than "Oh"? Let me explain. I had a friend from Ecuador when I was in Oxford. He was not of 'typical' South American looks, nor Hispanic, so I wondered, just out of curiosity, what his roots were. Turned out he was the offspring of a Spanish Catholic and a German Jew. When he told me this, I just said "Oh", or maybe it was "ah!" because that filled in my information gaps.
He said, "Is that all?!!!"
Puzzled, I said, "Yes".
It was the first time someone had simply accepted his delineation without "further complications". I think that meant he had experienced some negative feedback previously, though why is beyond me.
However, I do understand your reaction to obvious racism, and quite right too.