Leuco dye

A leuco dye (from the Greek leukos: white ) is a dye which can switch between two chemical forms; one of which is colorless. Reversible transformations can be caused by heat, light or pH; resulting in examples of thermochromism, photochromism and halochromism respectively. Irreversible transformation typically involve reduction or oxidation. The colorless form is sometimes referred to as the leuco form