F 1545 (OTTO) Fuchsin acid Cas no 3244-88-0 - used in Masson's trichrome stain. This method is commonly used to stain cytoplasm and nuclei of tissue sections in the histology laboratory in order to distinguish muscle from collagen. The muscle stains red with the acid fuchsin, and the collagen is stained green or blue with light green SF yellowish or methyl blue.