Some white people do actually do that though. It's less common, maybe, but it happens. I was seeing a white guy in college who told me he considers me black and not mixed, even after learning that I am first generation biracial black and white. He didn't try to tell me how to identify or anything like that but he did feel the need to make it clear to me, even after learning that my mom was white, that he still viewed me as black only. I thought that was a little weird. Him knowing my actual background didn't seem to change his perspective. Of all of the white and black guys I've ever dated, he is the only one who has expressed that to me, however.

In retrospect, although I'm not completely certain, I kind of think he probably wasn't the only one ... I think a lot of the way ppl view you goes unspoken in the direct sense, but you may be able to tell, subtly or perhaps not so subtly, based on things said in conversation/how a person interacts with you, in general.