Seeing colour
Metamerism
Two things can match in one light and clash in another. With only three cone types, the eye cannot see the whole spectrum.
Presented by ClearTrust Free for designers, students and the curious.
Metamerism is the name for two colours that look identical although the light coming from them is physically different. It happens because the eye reduces every mixture of wavelengths to just three signals. It is the reason screens and printing work at all. It is also the reason a jacket and trousers that match in the shop can look mismatched in the street.
Why it happens
Light can contain any blend of wavelengths, and a full description of it needs a long list of numbers. The eye records three. Many different blends give the same three, and those blends look exactly alike. A yellow made of a single wavelength and a yellow made of red and green light together are a matching pair of this kind, called metamers. Every colour on a screen is a metamer of the real thing. A photograph of a marigold sends the eye a quite different mixture of light from the flower itself.
When matches break
A surface's colour depends on which wavelengths it reflects and on which wavelengths the lamp supplies. Two dyes can reflect light differently and still match under daylight. Move them under a fluorescent tube or a warm bulb and the balance shifts by a different amount for each, so the match fails. This is a constant problem in car repair, in matching thread to cloth, in dentistry and in house paint. It is why tailors and sari sellers carry fabric to the shop door to check it in daylight.
Dealing with it
Industries that care about colour check samples in a light booth, a box with several standard lamps that can be switched in turn. A match that holds under daylight, shop lighting and a household bulb is safe. The surest fix is to use the same pigments or dyes in both items, because then they reflect light the same way and match under any lamp. Observers differ a little too. Two people with normal colour vision have slightly different cones, so a match that is exact for one can be faintly off for another.
Sources and further reading
- Metamerism (color) on Wikipedia
- X-Rite: What is Metamerism?
- Stanford Computer Graphics Laboratory: Colour matching
Original text by the Rang desk, written with AI assistance and checked against the sources above. Meanings of colour vary from place to place and person to person. If we have something wrong, tell us.