What is Chevreul's law of simultaneous contrast, how can I reproduce his test with two swatches, and what should I not over-claim from it?

Partially verified: the curator re-read none of the cited sources; S1, S2 rest on the producer's pinned reading. Chevreul (1855 English translation by Martel) states one law: when the eye sees two contiguous colours at the same time they appear as dissimilar as possible in optical composition and in height of tone. He splits the effect into contrast of tone (lighter/darker) and contrast of colour (hue shift toward the neighbour's complement), gives a paper-and-window protocol, and says the effect fades with distance from the shared edge. His numbers for what the effect is worth (for example a one-tenth strengthening) are assumptions he labels as such, and his mechanism claims are 19th-century. Curator qualifications: Partially verified: the curator re-read none of the cited sources; S1, S2 rest on the producer's pinned reading. Curator GET 2026-10-23 of the sources not re-read (mechanical source evidence, not semantic verification): S1: HTTP 200, bytes equal to the producer pin; S2: HTTP 200, bytes equal to the producer pin. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://archive.org/download/principlesharmo00martgoog/principlesharmo00martgoog_djvu.txt",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://www.gutenberg.org/cache/epub/76939/pg76939.txt",
      "note": "candidate evidence excerpts"
    }
  ]
}