This is from Kwame Anthony Appiah's In My Father's House: Africa in the Philosophy of Culture, p.11:
...there are arguments in the works of the pre-Socratic Sophists to the effect that it is individual character and not skin color that determines a person's worth.
He has an endnote that deals entirely with the first half of this sentence, which was about Homer. He gives no source for this claim, and there's no other mention of anything remotely helpful in the context.
This is a little surprising to me, because the only Sophists I know of who we have any record of what they thought about ethics were Protagoras in his relativism and Antiphon in his egoistic nihilism. I wouldn't expect either to put forward such a view as a genuine moral truth, and the others we have any indication about (Gorgias, Thrasymachus, Callicles) seem to have been with Antiphon at least in terms of the basic view.
So does anyone know of any information that Appiah must be aware of that I'm not?