Lab experiment
Odd One Out
One square is not like the others. Every level shrinks the difference and grows the grid, until your eye gives out. No photo needed.
Every square on the board is the same color except one. Tap the odd one and the next board is harder — the difference shrinks and the grid grows.
Three wrong taps ends the run. Each level has a known Delta-E, so where you stop is a measurement rather than a score: it is the smallest color difference you could actually see.
The difference is hue on some levels, lightness or saturation on others, and which one you are weakest at is the part worth finding out.