Reversible and stable photochromic plastic lenses were obtained using photochromic dyes that were mixed during the casting process of the lens. Photochromic lenses with blue, red, yellow, and gray dyes as well as different concentrations of blue dye were prepared. The initial colors and fading speeds of the different dyes and different concentrations were examined by measuring the transmittances of the colored and bleached lenses. The initial color increased slightly with increasing dye concentration but the contamination was not as severe as the commercial photochromic lens. The fading speed was measured by changing the concentration of the dye and it was independent of the dye concentration. The relative transmittance was found to be more convenient for comparing the photochromic properties than the absolute transmittance because it could be used regardless of the type of color and dye concentration.