Contrast Grid Optical Illusion

Is there any gray where the lines intersect?

See Another Random Optical Illusion

Scroll down for the explanation.

There is no gray, but did you notice the gray spots at the intersections?
Most people do. Neat, huh?

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 dark and light is so strong that the light area ends up looking gray.

You can read more about color perception here.