Gemological, spectroscopic, and chemical properties of diamonds treated using the new Serenity Technologies coating technique for inducing various “fancy” colors are reported. This technique produces intense blue, gray-violet, green, orange, pink, purplish pink, purple-pink, and yellow colors. The presence of a coating can be identified with magnification by observation of an interference-related colored (often bronzy) film, scratches, and colorless and/or dark areas on the surface of the pavilion facets. UV-Vis absorption spectra and chemical analysis provide confirmation of the treatment. Chemical analysis also revealed that the coating is a SiO₂ film doped with Au and/or Ag for blue, pink, and yellow coloration, or with a surface Fe₂O₃ film for orange. No evidence was detected of either chemical diffusion or implantation of foreign elements into the diamond. While the colors produced by this treatment are stable to some standard jewelry repair and cleaning procedures, they are not considered permanent.