Well, people who were going to classify me based on race and what it says for "party preference" on my voter registration card aren't generally open to being convinced of anything, in my experience. I've given both variations of the answer before: that I'm so white I'm provably related to a 17th century American colonial governor (literally true); or, that it's none of their damn business. As far as I can tell, both have had roughly the same effect, which is little to none.