The present invention relates to a method of bulk-dyeing partially crystalline plastics, which comprises processing a plastic comprising both a pigment containing at least one each of O H groups --C-- and --N-- , which are joined O H to one another as --C-N-- or are in conjugation with one another, said pigment is selected from the group consisting of Pigment Yellow 139, Pigment Violet 37, quinacridone pigments, disazo condensation pigments, isoindolinone pigments and 1 ,4-diketo-2,5-dihydro-3 ,6-diarylpyrrolo3 ,4-c pyrrole pigments of formula R7, Rs, R9 and R,IO are independently from each other hydrogen, halogen, cyano, carbamoyl or C1,-C4alkyl; and from 0.001 to 0.25 parts by weight, per part by weight of pigment, ofa colorant R1, R2, R3 and ~ independently of one another are hydrogen, halogen, R6,OR6 or SR6,R5 is hydrogen or linear or branched C,-C12alkyl, benzyl or phenethyl, and R6 is an apolar group which is unsubstituted or substituted one or more times by halogen or by OC1-C6alkyl, with the proviso that: If Rs is C2-C4alkyl, there are at least 6 carbon atoms in total in Rl' R2' R3' R4’ and R5; if R5is methyl, there is an alkyl or alkylene chain of at least 6 carbon atoms in R1, R2, R3 or R4,; or if R5 is hydrogen, R1, R2, R3, or R4 is R6, OR6 or SR6, and there are two alkyl or alkylene chains of at least 6 carbon atoms, or one alkyl or alkylene chain of at least 12 carbon atoms, in Rr R2R3 and/R.