Crystal violet is the deepest blue of all the methyl violets, and is satisfactory for most purposes for which methyl violet is used, including the metachromatic demonstration of amyloid. Its darker blue shade makes it the dye of choice for use in Gram's stain for the demonstration and primary classification of bacteria. Although it has been used in the past as a bacteriostatic agent for topical skin application, Aldrich lists this dye as a cancer suspect agent.

The name gentian violet is given to many of the dyes in this general group, and can not be relied upon to give any consistency in identification. It is preferable to avoid the name altogether.