RAL is a color matching system used in Europe. In colloquial speech RAL refers to the RAL CLASSIC system, mainly used for varnish and powder coating. In 1927 the German Reichsausschuss fur Lieferbedingungen und Gutesicherung" (State Commission for Delivery Terms and Quality Assurance) invented a collection of 40 colors under the name of "RAL 840". Prior to that date manufacturers and customers had to exchange samples to describe a tint, whereas from then on they would rely on numbers.
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One corner of a room painted red for example, may appear a different shade from the rest of the room. This is because colors reflect color and light, which slightly changes its appearance and the way our eyes perceive the color.