The Aethiop

THE PURCHASER of a black servant was persuaded that the color 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 the man to incessant scrubbings.  The
servant caught a severe cold, but he never changed his color or
complexion.

What's bred in the bone will stick to the flesh.