Abstract: A process is provided for coloring thermosetting resins, made by polyaddition reaction of a nucleophile with an electrophile, with a polymeric liquid reactive coloring agent suitable for incorporation in the resin with the formation of covalent bonds, said coloring agent having the formula:R-(polymeric constituent-X).sub.nwherein R is an organic dyestuff radical; the polymeric constituent is selected from polyalkylene oxides and copolymers of polyalkylene oxides in which the alkylene moiety of the polymeric constituent contains 2 or more carbon atoms and such polyeric constituent has a molecular weight of from about 44 to about 1500; and n is an integer of from 1 to about 6; and X is selected from --OH, --NH.sub.2 and --SH, said coloring agent being added in an amount sufficient to provide coloration of said thermosetting resin.