Violet Light

Lovecraft, ever the autodidact scientist, knew that the electromagnetic spectrum contained ultraviolet light and that this caused sunburn.

In 1801 Johann Ritter conducted experiments with silver chloride and a prism. He projected a beam of sunlight through the prism, which split the beam into the colors of the spectrum. He them put chloride in each color to see the outcome and the deep violet darkened the chloride. Ritter placed chloride in the lightless area just beyond the violet and it darkened as it were in a smoky fire. This was the ultraviolet or UV light.

In school Chrispy learned the acronym ROY G BIV or red, orange, yellow, green, blue, indigo, and violet as the colors of the visible spectrum (or rainbow). Botice that DotWH has "yellow, carmine (red), and indigo" (see below).

Just prior to Lovecraft's generation, most white American elites shunned suntan as a "common worker's appearance". This gave rise to "redneck" as a farmer who worked in the sun in a collarlesss shirt. In most Little House on the Prairie Books, we see sunbonnets used to keep skin white. The migration of many New Yorkers to Florida and other cultural changes reversed the effect and had many working class people pale and white (from working in sunless factories or coal mines) and the rich healthy and "Hollywood" tanned.

In any event, Lovecraft mentions in Dreams of the Witch House, "Once he met some friends who remarked how oddly sunburned he looked, but he did not tell them of his walk. ...

"He would be lying in the dark fighting to keep awake when a faint lambent glow would seem to shimmer around the centuried room, showing in a violet mist the convergence of angled planes which had seized his brain so insidiously. ...

"Brown Jenkin, too was always a little nearer at the last, and its yellowish-white fangs glistened shockingly in that unearthly violet phosphorescence. ...

"Looking up at the house from outside, he had thought at first that Gilman's window was dark, but then he had seen the faint violet glow within. He wanted to warn the gentleman about that glow, for everybody in Arkham knew it was Keziah's witch-light which played near Brown Jenkin and the ghost of the old crone herself. ...

"Gilman felt a nameless panic clutch at his throat. He knew that Joe must have been half drunk when he came home the night before; yet the mention of a violet light in the garret window was of frightful import. It was a lambent glow of this sort which always played about the old woman and the small furry thing in those lighter, sharper dreams which prefaced his plunge into unknown abysses, and the thought that a wakeful second person could see the dream-luminance was utterly beyond sane harborage. ...

"Reluctantly he continued up to his garret room and sat down in the dark. His gaze was still pulled to the southward, but he also found himself listening intently for some sound in the closed loft above, and half imagining that an evil violet light seeped down through an infinitesimal crack in the low, slanting ceiling. ...

"That night as Gilman slept, the violet light broke upon him with heightened intensity, and the old witch and small furry thing, getting closer than ever before, mocked him with inhuman squeals and devilish gestures. He was glad to sink into the vaguely roaring twilight abysses, though the pursuit of that iridescent bubble-congeries and that kaleidoscopic little polyhedron was menacing and irritating. Then came the shift as vast converging planes of a slippery-looking substance loomed above and below him - a shift which ended in a flash of delirium and a blaze of unknown, alien light in which yellow, carmine, and indigo were madly and inextricably blended. ...

"In the dazzling violet light of dream the old woman and the fanged, furry thing came again and with a greater distinctness than on any former occasion. This time they actually reached him, and he felt the crone's withered claws clutching at him. ...