INDIGO a.
blue dye. -- Indigo bird (Zoöl.), a small North American finch (Cyanospiza cyanea). The male is indigo blue in color. Called also indigo bunting. -- Indigo blue. (a) The essential coloring material of commercial indigo, from which it is obtained as a dark blue earthy powder, with a reddish luster, C16H10N2O2, which…