 Developing color by using oxidized developers was first suggested by German chemist Benno Homolka who, in 1907, successfully developed insoluble indigo-blue and red dyes on a latent image by oxidizing indoxyl and thio-indoxyl respectively.He additionally noted these developers could create beautiful photographic effects.The potential of oxidized developers in a color photographic process however, was first realized by another German chemist, Rudolf Fischer, who, in 1912, filed a patent describing a chromogenic process to develop both positives and negatives using indoxyl, and thio-indoxyl-based color developers as dye couplers in a light-sensitive silver halide emulsion.