I've got to leave to take a small hairy creature to the vets, but just wanted to pop in a few more things if I might.
Food Unit, you said, ". . . but a person denying the white/black binary that has been a historical justification for something as blatant as slavery, would be on very shaky ground with all the evidence to the contrary."
Ah, but my ancestors were all from North of the Mason Dixon line. Slavery was confined to the Confederate States. At least three of my ancestors fought in the Union Army to defeat the Confederacy and abolish slavery. What does slavery have to do with me?
All of those statements are true, bar the question at the end. Plenty of white folks in the US will claim that slavery was in the past and is irrelevant today. They'll point out that white indentured servants suffered slavery-like conditions. They'll insist that Africans sold other Africans into slavery, so it wasn't just white people were bad. There are as many "excuses" for denying the reality of slavery as there are white people who use them.
I totally agree that Aunt Rose was dead wrong in not accepting that African American women were "genuine" women like herself. But, her belief was unshakeable throughout her life, as perhaps yours is regarding trans people. Her beliefs were shored up for generations by laws, traditions, religion, the media, etc. Sadly, that's not yet been entirely erased.
I'm glad that as you say, "time is telling this suppressed truth about people of colour." I also hope that time will also "tell this suppressed truth about trans men and women."