Aniline Blue WS, also called aniline blue, China blue, or Soluble blue, is a mixture of methyl blue and water blue. It may also be either one of them.
Aniline blue or its constituents are used to stain collagen, as the fibre stain in Masson's trichrome.
It can be used in the Mallory's connective tissue stain and Gömöri trichrome stain. It is used in differential staining.