Polyester colorant concentrates containing; 1) a polyester supporting material; b) a colorant selected from the group of dyes and/or pigments; c) 0.1 to 2 parts by weight per part by weight of the colorant of copolyester comprising the reaction product from (A) of at least one aliphatic primary dihydric alcohol with 2 to 6 C atoms, and; (b) dicarboxylic acids selected from the group consisting of phthalic acid, terephthalic acid, isophthalic acid and/or sebacic acid. The copolyester is characterized by having i) a melting range between 120 and 160.degree. C., ii) a melting viscosity SV ranging from 12 to 126 Pa*s, measured at 190.degree. C. and 2.16 kg in accordance with ISO 1133, and iii) a melting viscosity factor SF ranging from -2.3 to -0.3 Pa*s/deg determined at a temperature increase ranging from 160.degree. C. to 240.degree. C. with a shear rate of 109 s.sup.-1. The inventive polyester colorant concentrates are particularly suited for spin dyeing polyester fibers and filaments.