Alas, Samantha, you're wrong.
There is no place in the brain where race resides whereas gender is based on structures in the hypothalamus
You may wish to acquaint yourself with some of the current clinical studies about gender identity.
Some children insist, from the moment they can speak, that they are not the gender indicated by their biological sex ... www.scientificamerican.com
To pick focus on a white woman passing black is taking on an edge case. Many black people pass white, but they do not do it in predominantly black nations where institutionalized racism is not an issue.
If the Scientific American article is too lightweight, I can give you some articles written for medical doctors. As an in-between, I suggest the Charlie Rose symposium on gender identity and its biological roots might help clarify how gender is different from race.