Should be "celebs you didn't know were part black" if we're using celebs like Alicia Keys and Slash as examples. The fact that none of these people would be considered white and are automatically just called black despite having a white parent is in itself a result of white supremacy and it dates back to slavery.
The one drop rule they used against us ended up working in our favor in many ways. Biracial people with black ancestry share some of the same racist, hateful experiences full blooded blacks go through a lot of the time, so they see themselves as one of us - increasing our numbers.
It's still fukked up though.