90%+ of Black people in the US have White ancestors (mostly men, likely non-consensual in slavery times). So did that ancestor of yours cease to be Black if they had a White parent and magically became Black again over time after marrying other Blacks? Do you really want us to erect some BS purity threshold for Black status? If someone is trying to pass or says "I'm not Black", I leave it alone and don't bother trying to claim them. But to say all mixed people can't be Black is the kind of BS they would love for us to think. So we can be bickering, divided, and ineffectual like most Blacks in Latin America hung up on that "Black or mixed" crap.
So the next time a hot sister with one non-Black parent starts flirting with you and says "I'm Black", make sure you correct her ok