Tuneable reverse photochromes in the solid state
(PHYSorg.com Chemistry)

Photochromes are dyes that change their colour depending on the light they receive. When light is switched off they can either remain in their photoinduced state (P-type photochromes) or turn back to their original state (T-type photochromes). T-type photochromes may colour when irradiated, bleaching when light is moved away (direct photochromism) or discolour under irradiation, recovering their colour in the dark (reverse photochromism).