A long time ago I was in the information business in Washington D.C. on a more or less freelance basis. I had a lot of casual friendships with people in who were sometimes good for information and as often just good to have a beer with. There was this guy Smitty who worked for a very important big law firm and sometimes had a information to share sometimes was interested in what I knew.
We met at the usual K-Street watering hole after work and after about the second beer Smitty always made the same little obligatory speech... "I don't know if I ever told you this," he would say, "but I'm black." After he told me the first time I noted certain facial features that might be construed as black, but in fact I grew up with Italian kids who had darker complexions and more arguably "black" features. Still Smitty's family, which had a close association with the civil rights movement, was one that could have "passed" and chose not to. Respect.
Three books on the subject of passing:
Sinclair Lewis, Kingsblood Royal: Published in 1947, this scathing satire caused something of a stir. Not unusual for Lewis. In this novel, Neal Kingsblood is a successful Minnesota businessman who discovers he is descended from a famous American explorer. He is not bothered by the fact that his ancestor is black, and the can't stop talking about it. The USA has a hard and fast rule on blackness. One drop of blood is enough, and it pertains in Minnesota as much in Crackertopia. It doesn't take long before our hero begins to suffer the consequences.
Philip Roth, The Human Stain: A college professor has been passing all his life. Then he makes a politically incorrect statement in a classroom and the students conclude he is a rascist.
Karin Tanabe, The Gilded Years, A novel based on the true story of Anita Hemmings, the first black woman to graduate from Vassar.