I didn't know that anyone would know your race when you vote, but apparently that's a part of voter registration in the south.
In learning that, I came across 538's discussion of possible reasons for disproportionate rejection rates, particularly in states that make you go through some hoops to fill out a ballot, which is going to be more difficult for new voters.
North Carolina Is Already Rejecting Black Voters’ Mail-In Ballots More Often Than White Voters’ | FiveThirtyEight