How it gets harder
Level 1 starts with 2×2 tiles and the grid grows up to 8×8. The lightness gap between the odd tile and the rest starts at 20 and shrinks by 13% each level, never going below 0.6. Lightness is measured in the OKLab color space (0 to 100), which is designed to match how bright colors look to people, so a given level is about equally hard whatever color comes up.
The "smallest lightness gap" on the results screen is the hardest difference you found. The lower the number, the finer the difference you spotted.
For a fair test
- Turn the screen brightness up and switch off night mode, blue light filters and battery saver.
- Sunlight on the screen hides differences between dark colors.
- Compare your results on the same device over several tries.
Is it a color blindness test?
No. The game asks you to find lightness differences within one hue, so it cannot tell whether you have a color vision deficiency. If that is a concern, an eye doctor can test you properly.