An alkali-resistant pigment composition is provided comprising (a) a C.I. Pigment Yellow 139 and (b) an adduct containing a compound of formula (II) or a tautomeric form thereof, wherein X is O, S or NR1; Y is O, S or NR1; the group -A-B— is selected from the group consisting of —CR2═CR3−, —CR4R5—CR6R7−, —CY—CR8R9−, —CX—NR10−, —CR11═N—, —CR12R13−NR14−and R1 is hydrogen, C1-C8alkyl, C3-C7cycloalkyl, C6-C10aryl or C7-C10aralkyl; R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12, R13 and R14 are independently of each other hydrogen, halogen, C1-C8alkyl, C2-C8alkenyl, or C6-C10aryl, or R2 and R3 form a benzoannellated ring; and/or a melamine- or pyrimidine-based compound, which is optionally substituted. The pigment composition may be used as colorant in various applications, especially in coloring high molecular weight organic material, for example, coating compositions, paints, printing inks, liquid inks, plastics, films or fibers.