These optical illusions almost certainly aren't new, but I discovered them for myself when some application accidentally exhibited similar behavior.
For the first illusion, stare at the black dot. Eventually, the moving bar at the left side will appear to change color from grey to blue.
For the second illusion, point at the white page background and concentrate on the blue square for several seconds. Without moving your eyes, move the mouse pointer onto the square, which will change color. Initially, the rectangle will appear to be white just like the background, or as even a brighter white. After a few seconds it will "fade" to be the grey it truly is. This seems to work better if the window is maximized.
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