The relevant scenario would be to run a black progressive against a white progressive, both of whom hold identical positions on the issues important to the black community. This would happen in a democrat primary (sort of like Hillary vs Obama).
The black electorate would, I suspect, go for the black progressive candidate by a significant majority (”we need to support the brother for the purpose of advancing the cause for future black candidates in the future”).
Steve Cohen (D-TN) runs against black candidates in Democratic primaries all the time. Majority black Memphis is 3/4 of his district. He’s won 4 primaries against black candidates. White Dem candidates in districts with substantial black populations don’t get a free ride - they can’t win without the black vote, and many aspiring black pols run just because they think that they have the black vote locked up in the primaries. They are mistaken. Blacks will vote for the candidate who is best able to get them freebies and racial preferences. This is why there are so many non-black owned businesses in the slums. There are any number of black businessmen who would love to run those stores and restaurants. But black consumers won’t pay more to patronize black-owned businesses, any more than they will support a black politician who can’t deliver the freebies and racial preferences to which they feel entitled.