Object Colours, Material Properties and Animal Signals

Colour is commonly regarded as an absolute measure of object properties, but most work on visual communication signals is concerned with colour differences, typically scaled by just noticeable differences (JNDs). Object colour solids represent the colour gamut of reflective materials for an eye. The geometry of colour solids reveals general relationships between colours and object properties which can explain why certain colours are significant to animals and evolve as signals. We define a measure of colour vividness, such that points on the surface are maximally vivid and the ‘grey’ centre is minimally vivid. We show that a vivid colour for one animal is likely to vivid for others, and highly vivid colours are less easily mimicked than less vivid colours. Further, vivid colours such as black, white, red, blue and light, unsaturated shades are produced pure or orderly materials. This kind of material needs to created and maintained against entropic processes that would otherwise degrade or destroy them. Vivid coloration is therefore indicative of ecological affordance or biological function, so that it is valuable to have attentional biases towards these colours regardless of any specific significance.