for mourning was a Roman custom (Juvenal, x. 245)
borrowed from the Egyptians.
in blazonry, means constancy, wisdom, and prudence. Black,
in several of the Oriental nations, is a badge of servitude, slavery,
and low birth. Our word blackguard
seems to point to this
meaning. The Latin niger
meant bad, unpropitious.
(See under Colours for its symbolisms, etc.).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894