How many of them actually do though? There's Black Panther, Black Manta and Black Lightning and who else?
I'm pretty sure even the story that did that revealed Manta was lying about this and was just manipulating black people for his own ends.like Black Manta, who wanted all the black people to live underwater.
That seems like a weird idea for a nickname. It would like Diana calling Superman "Apollo" as a nickname. I don't know if I would call it racist but it does seem... dumb. And Jefferson isn't the type of person who would like being compared to a god even if he does want people to respect him.
I already suggested removing her from the League, but Diana is pretty redundant on a team that already has Superman and the Flash. If redundancy is an issue, Cyborg is not the only victim of it.