Contrast Blocks Optical Illusion

Do you see gray anywhere in this two colored illusion?

See Another Random Optical Illusion

Scroll down for the explanation.

Did you notice the gray spots at the intersections?
You can make the gray go away by covering either side of a narrow row between the blocks with paper.

Explanation

The eye, which responds to an amazingly wide variety of light sources from moon light to direct sunlight, tries to adjust to the present light levels. In this optical illusion, the contrast between the black and white is so strong and irregular that the white ends up looking gray.

You can learn more about color perception.