Toluidine red is an organic compound with the formula C10H6(OH)(N2C6H3(NO2)CH3).

A dark red solid, the compound is classified as a azo dye consisting of a 2-naphthol group linked to a 2-nitro-4-methylphenyl substituent.

[3] Toluidine red is a traditional pigment, found in oil paints.

[4] Although once popular, it suffers as a pigment owing to "insufficient lightfastness and bleeding when incorporated into a paint system.

"[1] It is classified as carcinogenic, a property that it shares with many azo dyes.