Dyes can be classified in different ways:
in view of the structure of the reference chemical family:
Acridine, Anthraquinone, Arylmethane, Azo, Cyanine, Diazonium, Nitro and Nitroso, Quinone-imine, Azin, Indamine, Indophenol, Oxazin and Oxazone, Thiazin, Thiazole, Xanthene, Fluorene and Fluorone, Pyronin, Rhodamine and others.

by their chemical behaviour or nature:
  • Acid dyes are water-soluble anionic dyes that are applied to fibers such as silk, wool, nylon
  • Direct dyes are used on cotton, paper, leather, wool, silk and nylon at neutral pH and high ionic strength conditions.
  • Metalcomplex dyes are metal salts and complexes of acid dyes.
  • Mordant dyes (requiring a mordant which improves their fastness) are used for wool especially useful for black and navy shades.
  • Basic dyes are water-soluble cationic dyes that are mainly applied to acrylic fibers and in the coloration of paper.
  • Vat dyes, applied after reduction in alkaline liquor as leuco form and subsequent oxidation to the insoluble dye (for example Indigo for denim).
  • Reactive dyes, which are the best choice for dyeing cotton and other cellulosic fibers, bear substituents capable to react with the fibre substrate forming covalent bonds.
  • Disperse dyes are substantially water insoluble dyes supplied as a finely ground paste, used to dye polyester, nylon, cellulose triacetate and acrylic fibres in presence of specific auxiliaries.
  • Sulfur dyes are used to dye cotton with dark colors.