Lucent Diamonds has developed a new treatment process for natural type Ia diamonds that produces colors ranging from pink-purple through red to orangy brown, using a multi-step process that involves HPHT annealing, irradiation, and low-pressure annealing at relatively lower temperatures. Those stones that achieve a predominant pink-to-red or purple color are marketed as “Imperial Red Diamonds.” Gemological properties and characteristic spectra are presented for 41 diamonds, representing the range of colors produced thus far. These treated-color natural diamonds can be readily identified by internal graphitization and surface etching seen with magnification, distinctive color zoning, and reactions to long- and short-wave UV radiation. The color is caused primarily by the absorption of the (N-V)^- center, with further influence from the (N-V)⁰, H3, H4, and N3 centers. Other characteristic infrared and UV-visible absorption features include the H1a, H1b, H1c, 6170 cm^-1, and, frequently, 594 nm bands. This type of defect combination is not known in naturally colored diamonds.