Color-forming agents of the present formula ##STR1## wherein X denotes hydroxyl, alkoxy, alkenyloxy, aralkoxy, cycloalkoxy, aryloxy, acyloxy, alkylamino, dialkylamino, acylamino, aralkylamino or arylamino,R denotes alkyl, alkenyl or aralkyl,R.sub.1 denotes hydrogen, halogen or alkyl,R.sub.2 denotes alkoxy, aralkoxy, aryloxy or a radical of the formula ##STR2## Y.sub.1 and Y.sub.2 independently of one another denote alkyl, aryl, cycloalkyl or aralkyl or R.sub.2, with A in the o-position, forms a heterocyclic ring,a benzene ring can be fused onto the ring A, in the o-/m-position relative to R.sub.2, and the ring A and its fused-on rings and the cyclic and acyclic radicals can carry further non-ionic substitutents customary in dyestuffs chemistry,are used in thermoreactive papers and pressure-sensitive recording materials and for the preparation of highly concentrated solutions in organic solvents.