Abstract: The invention relates to the treatment (enhancement) of diamonds in order to give them different colors and can be used by the gem and jewelry trade. The technique consists in producing isolated substitutional nitrogen atoms, or C centers, in the crystal lattice of natural near-colorless-to-brown type Ia diamonds containing A centers or in the crystal lattice of natural near-colorless high-nitrogenous type Ia diamonds containing over 800 ppm of nitrogen in the form of A and B1 centers. Natural type Ia diamonds containing A centers are HPHT-treated in a high-pressure apparatus at a temperature exceeding 2150° C. and under a stabilizing pressure of 6.0-7.0 GPa. Then they are irradiated with 5·1015-5·1018 cm?2 2-4 MeV electrons and finally annealed in a vacuum at a temperature exceeding 1100° C.