A process for mass-coloring high molecular weight material, in which process a compound of formula or a tautomer thereof, wherein M1 is H, ½ M2, ⅓ M3 or NR4R5R6R7, preferably H, ½ M2 or NR4R5R6R7, especially H, M2 is an alkaline earth or transition metal in oxidation state II or an oxo-metal in oxidation state IV, M3 is Al(III), a transition metal in oxidation state III or an oxo-metal in oxidation state V, R1 is H or a non-ionic substituent, R2 is H or, independently of R1, a further non-ionic substituent, R3 is H, C1-C6alkyl, phenyl, CO—C1-C6alkyl or CO-phenyl, preferably H or CO—C1-C6alkyl, especially H, and R4, R5, R6 and R7 are each independently of the others H or phenyl, benzyl or C1-C6alkyl, which are unsubstituted or may be substituted by hydroxy or by halogen and in the case of C3-C6alkyl is uninterrupted or interrupted by O, is incorporated into the high molecular weight material before or during shaping. The colorations obtained have good light stability and thermal stability, especially in polyolefins.