Character biography.
That simple.
If we’re going to hear fictional characters can be any race then why shouldn’t fictional slaves on a plantation be white?
Slaves were black. Their blackness is inherent to their servitude.
James Bond is Scottish. There are black Scots, and there are white Scots. The color of his skin isn’t relevant to his character.
Lets put it this way. I would venture there are black members of the Secret Intelligence Service today who are Scottish. However, there were no white slaves.
Fail. Try again.