Anyone who has bought a navy suit under fluorescent department-store lighting only to discover in the parking lot that it is actually black — or worse, a muddy purple — has personally rediscovered a phenomenon that David Paterson tried to warn the industrial world about in 1901.

Paterson's Colour-matching on Textiles was a working manual for dyers and calico printers, aimed squarely at practical shop-floor problems. Its most striking feature was a coloured frontispiece plate showing the same swatches of dyed cloth twice, side by side, under two different light sources. The caption is matter-of-fact:

"This Plate illustrates the abnormal modification in some dyed shades under artificial light. See Chapter IX."

In the preface, Paterson lays out why this deserved a whole book of its own:

"The subject is a comprehensive one, comprising as it does the study of colour-perception, the qualities of daylight, the optical properties of the fibres and dyestuffs employed, and also the influences of artificial illumination on colour appearances."

What Paterson was documenting — with dyed patterns bound into the appendix so a working colourist could compare fabric-to-fabric — is now called metamerism. Two samples can reflect light in ways that appear identical under daylight, yet diverge sharply under gaslight, incandescent bulbs, or fluorescents, because the spectral output of each light source is different and the dyes reflect different portions of the spectrum. It is not an illusion or a rare edge case; it is baked into how pigments and human vision interact.

Paterson was not the first to notice this — dyers had grumbled about "gaslight shades" for decades — but his manual is a remarkably early attempt to treat it as a systematic problem rather than a mysterious nuisance. He anticipated by roughly half a century the standardised viewing booths (using calibrated D65 daylight and CWF fluorescent lamps) that the textile, paint, cosmetics, and automotive industries now consider mandatory. Modern colour scientists have entire ISO standards devoted to metameric index calculation. Paterson essentially wrote the practitioner's version in 1901, with actual dyed cloth glued into the back so you could see the effect with your own eyes under your own lamp.

The forgotten part isn't the phenomenon itself — it's the habit of skepticism Paterson was trying to teach. Victorian dyers were expected to internalise that a colour match is only valid under a specified light. Today most consumers have lost that instinct entirely. We buy foundation makeup under LED store lights, judge paint chips under warm household bulbs, and match socks in dim closets, then blame ourselves for the mismatch. Paterson's manual quietly insisted that the light source is half the equation — a piece of practical wisdom that would save shoppers real money if it were still common knowledge.

The next time a "black" shirt turns out to be dark brown in sunlight, remember: a Scottish colour chemist bound the warning into his book 124 years ago, with actual fabric samples, because he assumed no one would believe it otherwise.