Mallory's trichrome stain

Mallory's trichrome stain is a stain utilized in histology to aid in revealing different macromolecules that make up the cell. It uses the three stains: aniline blue, acid fuchsin, and orange G. As a result this staining technique can reveal collagen, ordinary cytoplasm, and red blood cells. It is helpful, therefore, in examining the collagen of connective tissue.

For tissues that are not directly acidic or basic, it can be difficult to use only one stain to reveal the necessary structures of interest. A combination of the three different stains in precise amounts applied in the correct order reveals the details selectively. This is the result of more than just electrostatic interactions of stain with the tissue and the stain not being washed out after each step. Collectively the stains compliment one another.

...
Wikipedia