Why The Same Colour Changes Under Different Light

A navy jacket and navy trousers can match in daylight and clash under office lighting. The garments have not changed; the light illuminating them has, and colour is a product of both.

Colour is reflected light, not a property of cloth

A dyed fabric absorbs some wavelengths and reflects others. What is seen is the reflected portion, which depends entirely on which wavelengths were present to begin with.

A light source missing part of the spectrum cannot produce those wavelengths in the reflection. The colour therefore appears different rather than merely dimmer.

Daylight contains a fairly complete spectrum. Artificial sources vary enormously in what they contain, which is why they render colour so inconsistently.

Metamerism is why matched items stop matching

Two fabrics can reflect identical amounts of visible light under one source while achieving that result with different dye chemistry underneath.

Under a source with a different spectral makeup, those different chemistries no longer produce the same reflection, and the match breaks. This is metamerism.

It explains the common experience of buying a garment to match something at home and finding it wrong on arrival. Nothing was mislabelled and both observations were accurate.

Warm and cool sources shift everything

Incandescent and warm artificial light is heavy in longer wavelengths, which lifts reds and yellows and flattens blues. Navy reads black and browns read redder.

Cooler sources do the reverse, lifting blues and greens and making warm colours look muted or greyish. Skin tones also shift noticeably.

Because most people dress under one kind of light and are seen under another, the mismatch is systematic rather than occasional.

Dark neutrals are affected most

Black, navy, charcoal and dark brown reflect little light, so what they do reflect carries proportionally more influence from the source.

This is why distinguishing navy from black is difficult indoors and easy outdoors. There is not enough reflected light indoors to make the difference visible.

Pale and saturated colours are more stable, because they reflect enough across the spectrum for the difference between sources to matter less.

The practical response is where you check

Any colour decision that matters should be made in daylight, near a window or outside. That is the reference condition and the one others will most often see.

Carrying the garment to be matched, rather than relying on memory or a photograph, is the other half. Screens introduce their own colour shift on top of everything else.

Where an exact match is impossible, deliberate contrast is more reliable than a near match. A near match that fails under one light looks like an error; a contrast never does.