Simultaneous Color Contrast

   Color vision operates like any of the other visual channels in that colors appearance is relative. When we look at a color, our brain detects not so much the color itself, but the contrast between the color and the colors surrounding it. This phenomenon is called simultaneous color contrast. (For more information see simultaneous contrast.)

	(click on the image to enlarge it for a better illusion) In the above picture, all four inner squares are the exact same color. However, following the principles of simultaneous color contrast, each square contrasts with its surroundings in a different way. As a result, the upper left square has a blue tint, the upper right a green tint, the botttom left a red tint, and the bottom right a yellow tint.

Adaptation

   The color channels also follow the principles of adaptation. When the eye is exposed to a very intense signal of a certain color, it desensitizes to that color.

	Close one eye and stare at this red block for thirty seconds to a minute. Afterwards, put your mouse over the image to turn it into a picture. Compare how the picture appears with each of your eyes. Since one eye has been desensitized to red, the colors appear different!

Spatial Assimilation

   Spatial Assimilation is nearly the opposite of simultaneous color contrast. When two colors are placed extremely close to each other, the eye loses the ability to distinguish between them. When this happens, the colors begin to follow the properties of color addition and meld into a third color.

	The background of this entire image is the same color red. Small dots of blue, green, and yellow have been added. Because the dots are so small, our eyes lose the ability to distinguish the dots from their backgrounds. As a result, the background appears to be four different colors: four reds, each tinted the color of its corresponding dots. Put your mouse over this image to make the dots (and the illusion) disappear!

   Spatial Assimilation is especially important in the modern world because it is the concept behind color TVs and computer monitors. Inside this monitor there are only three colors of lights: red, blue, and green. These lights are so small that it is impossible to see each color by itself. The red, green, and blue lights can appear to be millions of colors because they are so close to each other. For proof, look at a monitor or television (larger and/or lower quality work better) closely or through a magnifying glass and observe the individual tiny lights.

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