Greek sail decoration

[Dan Diffendale]

There's also the story about the ship that took Theseus and the other Athenians to Crete, that it was sent out with black sails of mourning, which were to be swapped for white sails on the return voyage if Theseus escaped. He forgot to swap them, and his father King Aigeus jumped into the sea out of grief, thinking his son dead.

If someone can track down Philostratus, Heroica, xx. 25, it's supposed to refer to the ship that sailed annually from Thessaly to Troy to sacrifice to Achilles with black or sable sails.