The present invention relates to an azo dye of formula wherein D is the radical of a diazo component of the benzene, naphthalene, diphenyl, thiophene, benzothiazole, benzisothiazole, thiadiazole, indazole, benzotriazole, pyrazole, anthraquinone, naphthalic acid imide, chromone, phthalimide or diphenylene oxide series, R1 is an unsubstituted or substituted aryl radical and R2 is an unsubstituted or substituted aryl radical, with the exception of the compounds of formulae (1a) and (1b) to a process for its preparation and to its use in a process for the production of mass-colored plastics or polymeric color particles, and in the dyeing or printing of semi-synthetic or synthetic hydrophobic fiber materials.