An active composition for a decoy which radiates spectrally as the active composition burns, contains an additive which is distributed in the active composition and which increases the ratio of the intensity of radiation emitted during combustion of the active composition in the wavelength range from 3.7 to 5.1 μm to the intensity of radiation emitted during combustion of the active composition in the wavelength range from 1.9 to 2.3 μm. The active composition contains a fuel having carbon atoms and hydrogen atoms, and an oxidizer for the fuel, containing oxygen atoms. The amount of the oxidizer being such that it is not sufficient for complete oxidation of the carbon, and the additive being a catalyst present in the form of particles that catalyzes a redox reaction.