So there's this rule. Quite a few people operate based on it. The One Drop Rule. It's typically, as I've experienced it, related to euros and Negroes. I myself can't even shake the habit despite knowing how problematic it is. It goes something like, if you have even a little *RECENT* African in you then you’re Black. Now, for many of us, the African in us is very apparent. But even if you’re passing (can pass as a white), you're technically Black.
It is my opinion that the one drop rule only perpetuates connotations that Black is dirty, evil, and blemishing. Just one drop is enough to taint the purity that is being white. Just a little piece of Africa in your DNA and you have been sullied. This is violence. It feeds the narrative and resulting fear (racism) of white extinction. It's also got some very Hitler master race tones to it. Black and white people are not dichotomies. We're not representations of supernatural forces eternally locked in a battle of good and evil.
"Being Black/Brown" is so much more than your genetics. And if you're passing, there's of course the question of to what degree do you experience "the struggle".
Racial and ethnic identity is complicated. But let's stop using methodologies that promote negative self image and conflict.
*I have to say recent because with these genealogical testing companies and what we know about ancient homo sapiens, the whites have been trying to columbus Black and other people of color identities.*