The so called Nissl's stain is monochromatic stain. Ther is just one basic dye like cresyl violet, thionin, toluidin blue or methylen blue used to stain the Nissl Substance of neurons. I is a regressive stain, that means the tissue will be overstained at first an the differentiated by in this case ascended alcohols.
Monochromatic dye is acrydine sometimes it is orange,it is single strands nucleic acids in some time it floroescing red glow if it interacts with double stranded nucleic acids then it can give green flurosence.