vat dye: a water-insoluble dye that is applied by reducing the dye to an alkaline form, applying the dye, then regenerating the insoluble dye by oxidation in the material; used for dyeing cotton
dye: a usually soluble substance for staining or coloring e.g. fabrics or hair
law of effect: (psychology) the principle that behaviors are selected by their consequences; behavior having good consequences tends to be repeated whereas behavior that leads to bad consequences is not repeated