Quoting Rabbi Jonathan Sacks (published posthumously, on Ki Teitse):
If we think less of a person because of the colour of their skin, we are repeating the sin of Aaron and Miriam – “Miriam and Aaron spoke against Moses because of the Cushite woman whom he had married, for he had married a Cushite woman” (Num. 12:1). There are midrashic interpretations that read this passage differently, but the plain sense is that they looked down on Moses’ wife because, like Cushite women generally, she had dark skin, making this one of the first recorded instances of colour prejudice. For this sin Miriam was struck with leprosy.
Instead we should remember the lovely line from Song of Songs: “I am black but beautiful, O daughters of Jerusalem, like the tents of Kedar, like the curtains of Solomon. Do not stare at me because I am dark, because the sun has looked upon me” (Song of Songs 1:5).
End quote.