Okay
This is straightforward and simple and I found no bugs. It shows a progressively more detailed screens of squares, and you tap the single one that is a very slightly different color. But to be honest it gets boring pretty fast. It could be switched up by maybe having the light square move around so you have to find it and catch it. Most of them I find immediately, but on some of the black ones I never could find the different square even if I took a screenshot and poured over it later. Would like an option to skip a board for a few seconds penalty or something like that. I had a bit of trouble with eye strain. If the background was not white nor black but a medium to light gray, that would help a lot.