Naphtol green in aqueous solution is a popular staining solution in histology used for specific labeling and differentiation of various tissue components. Naphtol green, an anionic triphenylmethane dye, binds to basic (alkaline) components in tissues, especially proteins, producing a green stain.

This solution is often used in combination with other staining agents in multiple staining processes (such as trichrome staining), where it excels in its ability to selectively stain collagen and other connective tissue components. Naphtol Green has high light fastness and provides long-lasting, stable staining that is readily visible under both light microscopy and fluorescence microscopy.