gules

n. heraldic red color, red color on a coat of arms

In heraldry, gules (pronounced with a hard 'g') is the tincture with the colour red, and belongs to the class of dark tinctures called "colours". In engraving, it is sometimes depicted as a region of vertical lines or else marked with gu. as an abbreviation.The term gules derives from an Old French word goules or gueules meaning "throats" or referring to the mouth of an animal (whence comes the English gullet). The mouth and throat are red, hence the transfer of meaning.For many decades, heraldic authors have believed that the term may have arisen from the Persian word gul "rose" (coming to Europe via Muslim Spain or brought back by returning Crusaders) , but according to Brault there is no evidence to support this derivation.
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n. gules

(n.)
The tincture red, indicated in seals and engraved figures of escutcheons by parallel vertical lines. Hence, used poetically for a red color or that which is red.
  

Heraldic color for red.