What this measures
A grid of identical tiles, except one. Find it before the clock runs out. The odd tile's colour difference shrinks as you progress, so this is a straightforward measure of colour discrimination threshold combined with visual search.
Two quite different abilities are being tested at once, and it is worth knowing which one is limiting you. If you find the tile the moment you look at the right area, your discrimination is fine and your search is the bottleneck. If you stare directly at it and still cannot tell, that is discrimination.
Why the last levels are genuinely hard
Human colour discrimination is not uniform. We are far better at distinguishing hues near the blue–yellow and red–green axes than elsewhere, and much more sensitive to differences in the middle of the brightness range than at the extremes. So two levels with the "same" numeric difference can feel very different.
Your display matters too. A cheap panel, a low brightness setting, or an off-angle viewing position all compress colour differences that a good screen would show you. If a level feels impossible, tilt your screen — if the answer suddenly appears, that was the panel, not your eyes.
Search strategy
- Do not scan tile by tile. Serial search is slow and the grid gets large. Let your eyes rest near the centre and use peripheral vision — an odd patch tends to "pop" without being looked at directly.
- Defocus slightly. Blurring the boundaries between tiles makes a region of slightly different colour easier to see as a blob.
- Sweep in bands. If nothing pops, cover the grid in horizontal strips rather than wandering. Wandering re-checks the same tiles.
- Trust a hunch. If a spot keeps drawing your eye back, it is usually right — your visual system detected it before you could articulate why.
If you consistently stall early
Struggling at the levels with large colour differences is worth a second look. Check your screen brightness and viewing angle first, since those explain most cases. If it repeats across devices, the colour check here uses Ishihara-style plates with brightness matched out, which is a cleaner test of hue discrimination specifically — and if that also comes out low, a proper colour vision test at an optometrist is worth the visit.
Frequently asked
Q. Does this diagnose colour blindness?
A. No. It is a game, your display is uncontrolled, and colour vision deficiency has
specific patterns that a single difficulty ramp cannot identify.
Q. Why does it feel easier on my phone?
A. Phone screens are often brighter and more saturated than laptop panels, which
exaggerates small differences. Compare a device against itself.
Q. Do older people do worse?
A. On average, somewhat — the lens yellows with age, which particularly affects blue
discrimination. The effect is gradual and unremarkable.
For the brightness-controlled version of the same idea, see the vision & colour check.