In heraldry, gules is the tincture with the colour red. It is one of the class of five dark tinctures called "colours", the others being azure (blue), sable (black), vert (green) and purpure (purple).
The Plantagenet coat of arms, gules three lions passants guardants or, origin of the Royal Arms of England
Coat of arms of the House of Savoy, gules a cross argent
The Royal Arms of Scotland Or a lion rampant Gules within a double tressure flory-counter-flory of the second
Coat of arms of Schwyz (stained glass, 1573), gules plain; the Juliusbanner with the Arma Christi inset is held by one of the supporters.
Tincture is the limited palette of colours and patterns used in heraldry. The need to define, depict, and correctly blazon the various tinctures is one of the most important aspects of heraldic art and design.
Canons from the chapter of Bruges, solemn winterdress in fur
Hatching guide by Jan Baptist Zangrius, 1600