Researchers are still unable to thoroughly explain these color-changing behaviors, which are known as thermochromism (a switch in response to heat) and a photochromism (a switch in response to light). Still, these diamonds all contain unusually high concentrations of hydrogen, as well as traces of nickel and nitrogen, in their crystal structure. This nitrogen-hydrogen complex could be responsible for the chameleon effect. Some experts believe that chameleon diamonds have luminescent and phosphorescent properties.