Methyl violets are mixtures of tetramethyl, pentamethyl, and hexamethyl pararosanilins (this last is also known as crystal violet or methyl violet 10B). Due to this, the particular shade differs depending on the amount of each present. The more methylated the dyes are, the darker blue the sample will be. Methyl violet 6B is usually darker than methyl violet 2B, and methyl violet 10B is usually even darker. Their commonest use is in Gram's stain for the demonstration and primary classification of bacteria. Methyl violets are metachromatic and are sometimes used to demonstrate amyloid.

The name gentian violet is often used for the dyes in this general group, but it cannot be relied upon for any consistency in identification. It is preferable to avoid the name altogether.