A positive photo resist is provided on a surface of a photo mask blank. Light is then exposed onto the photo resist to form a predetermined pattern of unexposed and exposed portions in the photo-resist. After development, the exposed portions are removed and ions are implanted to obtain a modulated ion density in the photo mask blank. The implanted ions become color centers which absorb a specific wavelength of light and the modulated distribution of the color substrates create the grayscale photo mask. The photo resist structure is finally removed to produce a grayscale photo mask.