Visually indistinguishable colour stimuli are described as being metameric.

  • Metameric stimuli are colour stimuli that are indistinguishable from one another because they evoke the same response by the three cone cell types on which human vision colour vision depends.
  • A class of metameric stimuli can be specified by a set of tristimulus values, defined as the “amounts of the 3 reference colour stimuli, in a given trichromatic system, required to match the colour of the stimulus considered”.
  • Perhaps the most important application of metameric stimuli is to be found in the use of tristimulus values used in additive colour systems.
  • The RGB colour model, for example, uses mixtures of red, green and blue light to produce the impression of a complete range of colours for an observer.