Just a few tidbits to chew on, from my own experience:

* I had a friend who was basically chocolate-brown in complexion, who went to a family reunion (one of those extended family things). When he came back, he told me that there was a large segment of his family who were very light complected and who had been, in his words, "marrying white" for generations. That is, they had been selecting partners based at least in part upon their skin color. Until fairly recently, "passing" as white wasn't unusual among very light complected people of partially African descent (I've always wondered if the woman who entered my family tree from Georgia in 1866 may have been a member of this group).

* When I worked at the VA hospital in Tacoma, WA in the early '80s, we received a racial/ethnic printout that said, among other things, that we had no Black (the term then in use) physicians. I went to one doctor that we had who was from Ethiopia (and whose skin tone was very dark and asked him to fill out the necessary form (Federal govt.-a form for every purpose) to correct this. He told me, in somewhat over-direct language, that "Black" meant "Negro", that term referred only to individuals from sub-Saharan Africa and he, as a direct descendant of the Queen of Sheba, was considered Caucasian. I slunk back into my bureaucratic hole.