Most of the racists I know think that the blacks are "preadamites" , less than perfect experiments leading up to the ultimate creation, Adan man. Thats a view held by "Identity" believers. There are those who are "serpent seed" believers, thinking that the Jews are a product of sex between Eve and Satan.
I think there are those who consider becoming black was a result of Jahs curse, but I havent had much to do with that branch of the White Racist belief system