Metamers

Colors that appear to be the same to an observer, but have different spectra.

For the Colorblind, Colors of Confusion are Metamers (e.g. blue and purple are metamers for red-green colorblind). Even for Color Normals, there are an infinite number of metamers, where light sources of different spectra appear to be the same color because they convert to the same tristimulus values in LMS Color Space.

One intriguing outcome of metamers in the Color Rendering Index. While a fluorescent light may be able to mimic D65 (standard white) in LMS, it is very different spectrally, making Daylight and Fluorescent light metamers. Since the interaction of an object’s Reflectance spectrum and an Illuminant’s spectrum occurs on a spectral level, the object can be perceived as different colors (LMS) under the two metameric Illuminants.