"The colors in this image should all look the same when viewed from a distance (on a system which assumes gamma = 2.2)":

Here's one for Macs (which assume gamma = 1.8):

The whole article is pretty damn cool, too: apparently most common software gets image scaling completely wrong. If you have a cheap LCD, this picture is fun:If you are using a low cost TFT display, the third column of two squares may show blueish, with a very different luminosity from the other squares and that luminosity also changes tremendously when you move your head up and down. These are gamma and color problems partially own to LCD technology and partially engineered on purpose to increase the brightness at the behalf of display quality. These gamma problems can partially be coped with using calibration hardware and/or software. I used xcalib to get an approximately correct display.
