On the measurement and classification of colour in studies of animal colour patterns

In studies of animal colouration it is no longer necessary to rely on subjective assessments of colour and conspicuousness, nor on methods which rely upon human vision. This is important because animals vary greatly in colour vision and colour is context-dependent. New methods make it practical to measure the colour spectrum of pattern elements (patches) of animals and their visual backgrounds for the conditions under which patch spectra reach the conspecific's, predator's or prey's eyes. These methods can be used in both terrestrial and aquatic habitats. A patch's colour is dependent not only upon its reflectance spectrum, but also upon the ambient light spectrum, the transmission properties of air or water, and the veiling light spectrum. These factors change with time of day, weather, season and microhabitat, so colours must be measured under the conditions prevalent when colour patterns are normally used. Methods of measuring, classifying and comparing colours are presented, as well as techniques for assessing the conspicuousness of colour patterns as a whole. Some implications of the effect of environmental light and vision are also discussed.