The principle of the chromogenic reaction and the transformation of "black and white" histochemical staining results or immunohistochemical signals to coloured microscopic images is described. The chromogenic reaction was optimized and is, so far, possible with either cyan-blue or magenta-red reaction products. The application of the chromogenic reaction to conventional silver stain was optimal in the Lendrum staining resulting in red or blue stained reticulin fibres. The Ag-NOR staining of the nucleolus organizing region (NOR) could be transformed by the same reaction to coloured reaction products as well as the silver-intensified immunogold technique in immunocytochemistry.