noun
or acid color
: any of a large class of dyes that contain acidic groups (as sulfonic or carboxyl groups) usually in the form of sodium or potassium salts, that are soluble in water, and that are used in an acid bath for dyeing especially textile fibers of animal origin and leather or in aqueous or alcoholic solution for staining cytoplasm and various acidophilic structures of cells and tissues — see dye table I