Color Perception Optical Illusion

How many colors are there in this picture, not including white?

See Another Random Optical Illusion

Scroll down for the answer and explanation.

If you answered two, you're absolutely correct.

Explanation

If you look closely, you will see that the apparently "new" colors in the middle are actually not new colors. They are a perceived change of the same colors which are used in other parts of the optical illusion. This affect occurs because the two colors are placed next to each other.

The darker colors you ”see” are an effect of “dithering.” Dithering is where the colors are printed so closely together that your eye mixes them to create a new color. The process of dithering is used extensively for color printing. If you look with a magnifying glass at a magazine picture, you will see how the full-color pictures are actually made from thousands of small dots using this color dithering process.