 The Uto paper came coated with a mixture of cyan, magenta and yellow dyes which appeared nearly black.It was sensitized with a catalyst that greatly increased the susceptibility of the dyes to fading.Where the coating was exposed to red light, that light was absorbed by the cyan dye and therefore bleached it, leaving the magenta and yellow dyes, which together appeared red; yellow light was absorbed by both the cyan and magenta dyes, bleaching them to leave only the yellow; green light bleached only the magenta, leaving cyan and yellow, which appeared green; blue light bleached only the yellow dye, leaving the cyan and magenta dyes, which in combination absorbed all colors of light except blue.