Aniline blue is a dye used for many purposes. However, sometimes we need to replace it with similar or alternative dyes. Some common synonyms for aniline blue include methylene blue, crystal violet, and toluidine blue. Methylene blue is closely related to aniline blue and can be used in its place for staining bacteria and other samples. Crystal violet is another closely related dye, and it can be used as a substitute for aniline blue in stain testing. Toluidine blue, on the other hand, is a slightly different chemical composition but can be used for the same purposes as aniline blue, namely staining cells, tissues, and microorganisms.