For creatures that emit or receive visual cues, body colors (or lack thereof) often serve key communication roles. In the context of predation, for example, conspicuousness in the form of blatant warning colorations can be a key to individual survival for both toxic prey organisms and their potential predators, whereas crypsis usually benefits prey that are highly palatable. In the context of sexual communication also, body colorations can influence genetic fitness through their rather direct impacts on reproductive success. Brightly colored males, for example, may tend to acquire more mates than their drab competitors, and hence be evolutionarily favored by sexual selection (see several sections below).

Colors are sensations of light induced in the nervous system of beholders by electromagnetic waves of various frequencies. In terms of biological effects, colors can be thought of as functional outcomes of mechanistic interactions between a transmitter and a recipient, so different observers may perceive the same object differently (for example, many pollinating birds and insects are highly attuned to ultraviolet flower colors that are invisible to people and most other mammals). However, colors also can be interpreted as the electromagnetic wavelengths themselves, in which case they become properties of the light source and the transmitting organism's reflective surfaces (irrespective of observer perceptions). In that sense, too, reflected wavelengths per se become another aspect of an organism's external phenotype. Regardless of how they are “viewed,” body colors have been the subject of a sufficient number of PCM analyses to warrant a separate chapter here.