I don't know about the Sttes, but elsewhere I'd think the negative connotations of "black" come from light and darkness and so forth, and that can carry over to ybnderpin prejuduce about shades of skin, rather than the other way round with negative attitudes towards "black" arising from prejudice against black people.

And the same goes for "red", starting with blood and arising out of that there being an impact on how people can think about red-hair or "red" skin. (Though the only people around who in fact do have genuinely red skins are people of Northern European ancestry who've been out in the sun.)
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The kinds of differences in assumptions Azizi mentioned that Americans appear to make along "racial" lines are disturbing, They echo the difference in political judgements, as demonstrated in the way that the Republicans have vanishingly little support among black Americans, and no doubt most of even that will have vanished in the wake of New Orleans. That kind of breakdown is profoundly worrying in any society.