HSL — Per-Color Hue, Saturation, Luminance
Adjust eight colour bands independently: shift skies bluer, pull greens back, lift skin luminance.
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Eight bands are weighted with a raised cosine window centred on each hue, so adjacent bands overlap smoothly. Hard band boundaries would produce visible colour blocks wherever a gradient crosses from one band into the next.
Near-neutral pixels are skipped. Below a small chroma threshold the hue of a pixel is essentially noise, and adjusting it would tint what should stay grey.