A big question in behavioural ecology is what drives diversity of colour signals. The dataset covers the testing of the context-dependent predator selection on prey coloration. In the first experiment, detectability of artificial visual stimuli to blue tits (Cyanistes caeruleus) was tested by manipulating stimulus luminance and chromatic context of the background. In the second experiment, the effect of two light environments on the survival of aposematic, colour polymorphic wood tiger moth (Arctia plantaginis) was tested. For detailed description of the material, methods, and results of the study, see the article