How it works
Every round shows a grid of tiles in one colour, except one that is slightly lighter or darker. Find it and tap it. Each correct tap moves you up a level: the grid gains tiles and the difference between the odd tile and the rest shrinks. By level twenty the gap is a fraction of a percent and you are mostly working from the corner of your eye.
You get sixty seconds. A correct tap adds one second back, a wrong tap costs three. The score is the level you reach before time runs out.
A trick that genuinely helps
Stop staring at individual tiles. Peripheral vision is much better at spotting a difference across a whole field than central vision is at comparing two things in sequence — so defocus slightly, look at the middle of the grid, and let the odd tile announce itself. Most people improve by several levels the moment they stop hunting tile by tile.
It also helps to turn your screen brightness up and avoid direct sunlight. At the higher levels the difference is smaller than the error introduced by a dim or glary screen, which means you can be looking straight at the answer and not see it.
Is this a colour blindness test?
No, and it is not designed as one. The odd tile differs mainly in lightness rather than hue, which means it stays playable if you have red-green colour vision deficiency — a test built on hue alone would be unplayable for roughly one man in twelve. If you want an actual assessment of colour vision, that is a job for an optician with properly calibrated plates, not a web page on an uncalibrated screen.
What the score means
Very little, honestly. Screen quality, brightness, viewing angle and ambient light all move the result more than eyesight does, so comparing your number against a friend on a different phone is comparing phones as much as eyes. Comparing your own score across attempts on the same screen is more meaningful — and most people climb several levels in their first few goes purely from learning to look differently.
Is anything stored?
Your best score is saved in this browser on this device, and nothing else. No account, no server, nothing uploaded. Clearing your browser data resets it.