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Two photochromic mixed fulgide single crystal systems showing multicolor photochromism and enhanced fatigue resistance were prepared with isostructural molecular pairs containing methyl-chloro and methyl-bromo groups. Parent crystals p-methylacetophenylisopropylidenesuccinic anhydride (1E), p-chloroacetophenylisopropylidenesuccinic anhydride (2E), and p-bromoacetophenylisopropylidenesuccinic anhydride (3E) showed light magenta, brownish orange, and orange colors, respectively, upon irradiation at 365 nm. Each two component mixed crystal MIX-1E and MIX-2E composed of 1E/2E and 1E/3E in a 0.39:0.61 and 0.88:0.12 ratio, showed four different colors upon irradiation with UV light and visible light of appropriate wavelengths. Further, it was found that colors of mixed crystals can be fine-tuned to impart different shades of colors over a range of four distinct colors shown by each, upon changing the length of the time irradiated at selected wavelengths. Such multicolored photochromic systems can be used to dev...