Origin of "Lily-Livered"

This terms comes from the ancient Greeks. They used to sacrifice an animal before going into battle, and inspect its liver as an omen of how successful fight would be. If the liver was red, it was a good omen. But when the liver was pale, it meant bad news for the battle.
Since the outcome of any battle was largely dependent on the bravery of the troops, by extension the liver of a coward was thought to be as pale as a lily. And this is the reason a coward was regarded as lily-livered.