A dye in any of three clearly defined chemical classes: (1) nitroarylamine; (2) azo; and (3) anthraquinone; almost all contain amino or substituted amino groups but no solubilizing sulfonic acid groups. They are water-insoluble dyes introduced as a dispersion or colloidal suspension in water and are absorbed by the fiber, after which they may remain untreated or be after-treated(diazotized) to produce the final color. Their use is primarily for cellulose acetate, nylon, polyester, and other synthetic fibers, and for thermoplastics.