White's Optical Illusion

Below is an excellent example of White's illusion. This is an interesting effect, below there is only one shade of gray, one shade of blue and one shade of red (to be clear all of the gray you see is the exact same color, this applies also to all blue and all red you see).

Although the color lines on top appear to be darker than the color lines immediately below, they are actually identical. That is, they are identical in intensity, but perceptually different in lightness.

As you can see, the color lines on top are mostly surrounded by black, while the color lines below are mostly surrounded by white. The color lines' surroundings are changing their perceived color.