If you do this in a fullscreen browser on a widescreen monitor, your peripheral vision will also come into play. You'll be able to see that the edges of the mon

If you do this in a fullscreen browser on a widescreen monitor, your peripheral vision will also come into play. You'll be able to see that the edges of the monitor are slightly different color than the center, because peripheral vision is less good at seeing color. When I shrunk the monitor down to a narrower window, I was getting more consistent results than otherwise.