E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
An heraldic term. The most honourable heraldic colour, signifying valour, justice, and veneration. Hence it was given to kings and princes. The royal livery of England is gules or scarlet. In heraldry expressed by perpendicular parallel lines. (Persian, ghul, rose; French, gueules, the mouth and throat, or the red colour thereof; Latin, gula, the throat.)
With mans blood paint the ground, gules, gules.