sinsboldly wrote:
http://en.wikipedia.org/wiki/One-drop_rule
The one-drop rule is a historical colloquial term in the United States that holds that a person with any trace of African ancestry is considered black unless having an alternative non-white ancestry which he or she can claim, such as Native American, Asian, Arab, or Australian aboriginal.[1] It developed most strongly out of the binary culture of long years of institutionalized slavery.
Apparently, from what I have heard, and the article, the one drop is to get rights under the law. I don't think people consider one with less than 1/16 of a given race to be that race. Even a black would have gone 4 generations without showing any sign of being black, so they likely aren't, in any way that would encourage racism.