How did coats of arms influence the colours of many European national flags?

Following the introduction of heraldry to Europe in the 12th and 13th centuries, European royalty adopted coats of arms that served as the foundational basis for many national flags. While the specific heraldic devices themselves have largely disappeared from most modern national flags, the colours originally used in those coats of arms were retained and continue to define the flags of nations such as Poland, Belgium, Germany, Spain, Hungary, Luxembourg, and Monaco.1

In the context of heraldic design, these colours—referred to as tinctures—consisted of metals (gold/yellow and silver/white) and specific colours, primarily gules (red) and azure (blue). These tinctures were governed by rules of visibility, which generally prohibited placing a colour upon a colour or a metal upon a metal to ensure the designs remained distinct and recognizable, a principle that influenced the aesthetic clarity of early flag designs.23