BLUE, one of the seven colours into which the rays of light divide themselves when refracted through a glass prism. For an account of the particular structure of bodies by which they appear of a blue colour, see the article CHROMATICS.—The principal blues used in painting are Prussian blue, bico, saunders blue, azure, or smalt, verditer, &c.; for the preparation of which, see COLOUR-Making.—In dyeing, the principal ingredients for giving a blue colour, are indigo and woad. See DYEING.
BLUE Colour of the Sky. See SKY.