Field note · 3 min read
The light in the room is a variable
In short
Two fabrics that match under a shop's lamps can separate the moment you step outside. That is metamerism, and it is not your eyes failing.
Two colors can reflect light differently across the spectrum and still look identical under one light source. Change the source — tungsten to daylight, warm LED to cool LED — and they come apart. Color scientists call this metamerism, and it is the reason color work is specified against standard illuminants such as the CIE's D65, an average daylight reference.
For an analysis this has one blunt consequence: do it in daylight, near a window, with the light on your face rather than behind you. A warm bulb pushes everyone toward looking golden and healthy, which is flattering and completely useless as evidence.
The same applies to selfies. A phone's auto white balance is actively trying to neutralize the color cast you are attempting to measure. Shoot in even, indirect daylight, and take the photo twice.
Sources
Every summary here was written for Percol; nothing is copied from the works cited. The sources are named so a reader can go and check the original.
- International Commission on Illumination (CIE), standard illuminant D65
- Faber Birren, Color Psychology and Color Therapy (1950)
More reading
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Hair colour is almost entirely a lightness
Every natural hair colour on earth absorbs inside a twenty-nanometre band. What varies is how dark. Everything a salon argues about after that is a correction — bought with the reagent that costs you the fibre.