Photochromic sapphires show an optically controllable orange coloration under ambient temperature, which strongly affects the color appearance and market value of gemstone sapphires. An in-situ absorption spectroscopy combined with a tunable excitation light source has been developed to investigate the wavelength- and time dependence of sapphire’s photochromism. An excitation of ≤370 nm and ≥410 nm introduces and removes the orange coloration, respectively, accompanied by a stable absorption band at 470 nm. Both the color enhancement...