New methods of forming color-coated gemstones are provided. These methods broadly comprise subjecting a source of metal (e.g., an organometallic compound) to a vapor deposition process so as to form the metal source into a vapor that is subsequently deposited onto the surface of a previously heated gemstone. The vapor is also diffused into the gemstone so as to form a mixed zone of gemstone having the metal source dispersed or intermixed therein. The coated gemstone is then subjected to heat treatment to alter the valence state of the metal in the coating until the desired colored coating is obtained, resulting in coatings having superior adhesion and optical properties.