a heat sensitive recording member capable of acquiring a stable color in selected regions contrasting with the background color of the coated substrate upon exposing these regions to an elevated temperature and comprising a paper or polymeric film substrate and a heat sensitive coating comprising an adduct or mixture of color - forming lactones or spiropyrans with a cyclic polyketo color precursor , a polymeric binder which bonds the reactants to the substrate and optionally a molecular complex between a phenolic compound and an amine and / or an activator to lower the temperature of color formation .