People of color were certainly repressed during this time frame, but not because of punitive tax rates on the highest incomes.

I can't think of any mechanism wherein people of color in the 1940s through the mid 1960s would have been better off if rich people were taxed lower. So, I would have to disagree with your assessment: The confiscatory top-tier tax rate did, indeed, benefit people of color, just not nearly enough to offset the harms of legislated segregation and institutional racism.