This CSS crime uses easing functions not supported by some browsers. If the black square below does not move, please expand the post to see an alternative version that should work with all browsers.
Stare at the dot in the center without shifting your gaze. Eventually the colored dots should seem to vanish and be replaced by periodic flashing of the original dot's opposite color.
I find it that the illusion appears quicker and more reliably if I view it with one eye closed, with my head quite close to the screen. Your mileage may vary.
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In the dark variant, the dots end up losing their color and start flashing with a dark color. The RGB values of the dots are the same as in the light version.
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A grid of blurry colored dots can be seen. The dots are animated so that they periodically disappear and reappear quickly. A small black dot is present in the center of the grid. By staring on the black dot the colored dots seem to vanish and are replaced by a dot that periodically flashes with the opposite color of the original dot.
Alternative variants under the fold for browsers that do not support the animations above: