Metamer:
In colorimetry, metamerism is a perceived matching of the colors that, based on differences in spectral power distribution, do not actually match. Colors that match this way are called metamers.
A spectral power distribution describes the proportion of total light given off (emitted, transmitted, or reflected) by a color sample at each visible wavelength; it defines the complete information about the light coming from the sample. However, the human eye contains only three color receptors (three types of cone cells), which means that all colors are reduced to three sensory quantities, called the tristimulus values. Metamerism occurs because each type of cone responds to the cumulative energy from a broad range of wavelengths, so that different combinations of light across all wavelengths can produce an equivalent receptor response and the same tristimulus values or color sensation. In color science, such sensations are numerically represented by color matching functions. [Wikipedia]
Which helps me make sense of where I saw it in use, which is “Special glasses give people superhuman colour vision,” Chris Baraniuk, NewScientist (25 March 2017):
IT’S sometimes practically impossible to tell similar hues apart, even placed side by side. Special glasses could improve our ability to do so, and could one day help to spot counterfeits.
Devised by a team at the University of Wisconsin-Madison, the glasses basically enhance the user’s colour vision. They allow us to see metamers – colours that look the same but give off different wavelengths of light – as recognisably distinct hues.
Human colour vision relies on three types of cone cells that react to short (blue), medium (green) and long (red) wavelengths. While brushing up on his knowledge of the eye before teaching a photonics class, physicist Mikhail Kats had a brainwave. Could the eye be tricked into effectively having another type of cone cell?
To make the glasses, Kats and his colleagues designed two colour filters, one for each eye, that strip out specific parts of the blue light spectrum. The team hypothesised that giving each eye slightly different information about blue things would simulate a new set of blue cones, making any subtle colour differences more pronounced. They were right (arxiv.org/abs/1703.04392).
They tested the effect using blocks of colour, displayed on a computer and smartphone screen, that people see as metamers. “They look exactly the same, and you look through the spectacles and… holy crap, they’re two different things,” says Kats.
Although I still think the summary of metamer in here is still clumsy and confusing. I would have said, colours that look the same but are composed of different wavelengths of light.
