Color fading of tablets colored with Eosin, Light Green SF, or Tartrazine was examined by the irradiation of high-pressure mercury vapor lamp in the fade tester. A series of sharp-cut glass color filters were used to examine the effect of intensity of light. Changes in surface color were traced by a colorimetric method using the integrating sphere-type color difference meter. The chromaticity coordinates, a, and b, and lightness, L, in the Lab system changed exponentially with increasing exposure time. However, no functional relationship was obtained between these values and illumination, or radiation energy of the lamp. Stability to fading was evaluated using Hunter's color difference formula, and compared by the acceptable color difference. Eosin and Light Green SF had poor stability, while Tartrazine was very stable. It was confirmed that the intensity of ultraviolet rays mainly contributed to the fading, but that the visible light with longer wavelength was also responsible.