In order to alter their original color, diamonds can be irradiated using a nuclear reactor and controlled heating known as "annealing". This improves the color of the diamond, to make it appear the same shade as natural fancy colored diamonds such as yellow, blue, green, brown, and pink diamonds. Sophisticated equipment, such as an infrared spectrometer, is needed to identify the origin of color.

Today diamonds are color treated in an electron accelerator where they are exposed to a stream of electrons turning the diamonds to a greenish hue. Then through a heating process the stones are annealed to the yellow, orange and brown colors. The diamonds do not become radioactive in this treatment and therefore can be used in jewelry immediately after the color change process.

Basically, the radiation bombards the atoms in the gemstones, knocking them either out of the stone, or moving them around inside the stone. The removal from the stone, or relocation inside the stone, causes the stone to react to light differently, which causes the stone to offer a different color.