One of the mysteries of the English language finally explained.
A substance to which the colour of a natural substance or object is due, or which is used to impart colour in a manufacturing or artistic procedure; a pigment, a dye.
Late 17th century; earliest use found in William Salmon (1644–1713), medical empiric and author. Partly (probably originally) from colouring + matter, and partly from colouring + matter; compare discussion at -ing.
colouring matter/ˈkʌl(ə)rɪŋ ˌmatə/
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