Sort each row into a smooth gradient between its two pinned end caps (marked •). Drag a tile, or tap one and then tap where it belongs. Keyboard: Tab to a tile, Space to pick up, ← → to move, Space to drop.
Neighboring tiles differ by about ΔE₀₀ 3.
A game for training your eye, not a medical color vision test. Screen brightness, color calibration and room light all change the result.