Visually indistinguishable colour stimuli that appear the same but have different spectral compositions are called metameric.

  • Metameric stimuli are colour stimuli that are indistinguishable from one another because they produce the same responses from the three types of cone cells in the human eye that are responsible for colour vision.
  • Metameric matches can occur in different parts of the spectrum, which means that the spectral power distributions of different light sources can look similar, but not identical, to one another.
  • A class of metameric stimuli can be specified by a set of tristimulus values, which represent the amounts of three reference colours, typically red, green, and blue, in a given trichromatic system, that are required to match the colour of the stimulus considered.
  • The most important application of metameric stimuli is in the use of tristimulus values for additive colour mixing, such as in computer displays and TVs.
  • The RGB colour model, for example, uses mixtures of red, green, and blue light to produce a wide range of colours visible to an observer.