Three Hundred Æsop's Fables/The Æthiop
The purchaser of a black servant was persuaded that the colour of his skin arose from dirt contracted through the neglect of his former masters. On bringing him home he resorted to every means of cleaning, and subjected him to incessant scrubbings. He caught a severe cold, but he never changed his colour nor complexion.
What's bred in the bone will stick to the flesh.