An agent for preventing the fading or discoloration of coloured images produced by using a color former, the agent being a transition metal salt or zinc salt of a saturated or unsaturated lower aliphatic hydroxycarboxylic acid, a saturated or unsaturated lower aliphatic dicarboxylic acid, an aromatic dicarboxylic acid or an aromatic hydroxycarboxylic acid, is added to the heat - or pressure - sensitive material containing the color former. The preferred stabilisers are Zn and Ni salts of hydroxynaphthoic acids added to heat-sensitive materials containing colour formers such as crystal violet lactone.
