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Complementary Colors and Simultaneous Effect

Opponent colors on a color wheel are called complementary colors. A complementary color complements another color so that they give white (with light colors or RGB-colors) or black (with object colors or CMY-colors). Example: The complementary color of magenta is green. When mixing a color paste of pure magenta with a color paste of pure green, we obtain black. We obtain white light when magenta-colored light and green-colored light are overlapping.
When speaking about contrast, we almost automatically think of the colors black and white. But just as snow emphasises the wintry contours of trees, the simultaneous effect of colors can intensify color contrasts, increase their colorfulness. Complementary colors affect each other in such a way that they appear brighter and more intense. The following illustrations demonstrate the simultaneous contrast. You just have to fix your eyes on the cross between the squares for some seconds and perceive the squares only "in the corner of the eye":


You can see that the small, medium-gray square appears darker on a white background than on a black background, although it is the same hue of gray.
When the squares are selected with the mouse, the black background disappears - when the mouse is moved away, the background reappears. Note: Due to the fact that you have fixed your eyes on the cross, so-called "afterimages" occur. These afterimages will last a while, possibly several minutes. Nevertheless, the gray hues seem to be unequal in color at first glance; so you better have a little break, look somewhere else and go back a few steps, and only then you will see that the squares are equal in color.
Now a similar test with colored squares. The colors have been darkened a little bit so that they won't shine too much on the computer screen:


When staring at the cross, we see that the red on the left seems to be more intense. But turquoise and orange have the same brightness; so this cannot be the same effect of increase in contrast that we have observed in the black and white test. This new effect, i.e. that colors intensify each other, is called complementary contrast or simultaneous contrast.

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