As often happens, a student's paper will lead to research down a previously unknown path and such was the case recently with the odd lawsuit of Susie Phipps.
In 1896 in Plessy v Ferguson SCOTUS ruled that separate equal facilities were OK. Home Plessy was 1/8 black, an octoroon. In 1982 Susie Phipps challenged a Louisiana law that defined a person having 1/32 black blood as "colored." Current SCOTUS practice has permitted such classifications when if the state has a compelling interest or if used to correct an injustice.See http://www.mixedracestudies.org/wordpress/?p=12475
This kind of racial minutia which was originally used to deny people equal rights is now being used proactively to define new rights. See this very interesting essay: http://jonathantilove.com/mutability-of-race/
I should note a personal anecdote. My son is adopted and was abandoned as a child. He self-identifies as black and is most likely a wonderful combination of all sorts of races. He married a white woman and they had a child. At the hospital, the child's race was identified as white on the birth certificate until he walked into the room and then they erased it and changed it to black. Now if race is so arbitrarily defined, perhaps it's time to get beyond it.
And for some, now, especially those in the diversity industry, it has become an advantage to perpetuate racial designations. A book on the topic I recommend is Michael Benn Michaels' The Trouble with Diversity: How We Learned to Love Identity and Ignore Inequality.