Thespian Hoplites and black armour

[Dan Howard]

Why would an artist depict a black faced Corinthian, not only this particular vase but several others, if he had never seen one?

Obviously because that was the only colour available to the artist on that particular medium. It is a monochrome illustration - the only intention is to differentiate different parts of the drawing. It is unreasonable to pretend that we know what colours the various items on those drawings are.