That is the whole difficulty of Color Sense Test: one tile on the grid is shifted by twenty-five values per channel, and you have twenty seconds to keep finding it. The scope on the monitor plots both shades at once — they land on top of each other.
Source A — every cell is one shade but one. The odd cell is off by 25 of 255 on each channel, in a direction nothing marks.
The monitor above is the whole game, running in this page. No download, no sign-up, no account: a grid of tiles carries one shade, one tile does not, and you have twenty seconds to find it. Color Sense Test — colour, if you spell it that way — is the same board the phone app runs, put on the web so you can try it before you install anything.
Two sources, two ways to be wrong. Source A is the find-the-different-color grid: every tile is one shade but one, and the odd tile is off by 25 of 255 on each channel, in a direction nothing marks. Source B puts the target on the reference bars above and below the grid and asks you to match that exact value off them — slower work, which is why it grades a few levels lower.
Nothing about the shift changes as you climb. What changes is the board: 4 tiles, then 9, 16, 25 and 36 at levels 5, 10, 18 and 30, on a clock that starts the moment you get the first tile right and never resets. A wrong tap costs you nothing but a shake. Your score is levels cleared, and it plays the same on a phone as it does on a desktop screen.
The app returns a verdict the instant the clock stops. These are its own words, rung for rung.
Rungs shown for Source A. Source B grades the same lines a few levels lower — matching an exact value off a reference bar is slower work than resolving a shift.
The monitor above is the whole game. The app is the game plus what a run is worth keeping for: a global leaderboard per source, a username to climb under, your own colors on the chrome, and a haptic answer on every cell you touch.
Straight answers, starting with the one that matters most: no, this does not measure your eyesight.