How about refusing a shidduch due to race?
depends on the reason
Back to the Afrikaner's for a second
they believe they were the second coming of the Israelite's and the Trek was G-d taking them in the desert to the promised land and took the bible very literally. they looked to the Bible for every answer. Black were the children of Ham and therefore as you said, cursed, and slaves. They didn;t (dont) hate the blacks, they just believe that this is G-ds given mandate and the blacks must submit to be slaves as it is G-ds will.
So not for an Afrikaner to marry a black would be a problem as you said בני ברוך ואתה ארור ואין ארור מתדבק בברוך
Their main problem was they didn't know how to deal with the "coloured" issue and that was their downfall, they went waaaay overboard in trying to keep their "race" pure and blamed it on the Bible
(Michener explains it very well)