An imaging medium comprises a substrate carrying a color-change layer. This color-change layer comprises two layers or phases comprising two color-forming reagents which react upon heating to cause a change in the color of the layer. The color-change layer is deactivated by exposure to actinic radiation such that after deactivation it no longer undergoes its thermal color-change. The color-change layer is detachable from the substrate by heating to a temperature lower than required to cause the color change, so that upon contact of the imaging medium with a receiving sheet each individual pixel of the color-change layer may be left attached to the substrate, transferred to the receiving sheet but left uncolored, or transferred to the receiving sheet and colored to a color level determined by the energy used in the associated thermal print head element. The medium may be imaged by imagewise heating, followed by blanket exposure to deactivating actinic radiation, or by imagewise exposure to the actinic radiation, followed by heating of the whole color-change layer.