The embodiments of present invention provide method for imparting tone-controlled colors into colorless crystals such as gemstones or decorative objects by coating a atomically mixed thin film comprising of a color causing reagent and a toner material onto the surface of colorless gemstones or transparent crystals and subjecting them to a heat treatment to produce colors of desired shades in the crystals. The method employed is radiation-free, eco-friendly and avoid the use of any hazardous material. The method highlights that controlling the amount of toner material could easily control the shade of color induced by the colorant material. The coating of atomically mixed single film onto the surface of crystals results in reduction of diffusion time significantly at a reasonable temperature, to impart colors to crystals such as gemstones and colorless decorative objects.