LOL, I usually just answer "American" but saying of European ancestry isn't that eludicating either. I think the Europeans in general were pretty much mixing with everyone they could find by the late 1400s.
But, heck, the story of the Indo European languages is all about one tribe conquering another and assimilating their languages until we got Indo-European or "Caucasian" everything.
God knows what is mixed up in that supposedly pure whiteness....probably a lot of Asian, since the Indo Europeans conquered into Mongolia and got them all pissed off at one point.
People who talk about a "pure white race" make me laugh, especially if they're American. It tickles me to think that statistically, a third of Neo Nazis or KKK members have some African or Native American ancestry, no doubt. Probably some Jewish in there too, like I do in my German bit of ancestry, oh horrors!