Abstract
As known for centuries, if a small grey test patch is placed on a colored background, the test patch will be perceived as the color complementary to the color of the background-simultaneous color contrast. However, this same color is perceived for test patches if the background is acting upon the test patch by “pulling out” or removing from the test patch the color of the background. Interestingly, if the test patch itself is colored these two possible actions of the background on the test patch no longer produce the same perceived color for the test patch. We present a most compelling display in which the test patch is a long and relatively narrow color “gradient strip” moving from an intense solid color at one end with increasing amounts of white added until the other end is pure white. When this test patch is placed on a background of the same color as the gradient-e.g., a red to pink to white gradient strip on a red background-the entire strip is “bleached” in that the pure color appears whitened and the place at which the strip appears white comes far before where it is perceived as being when the strip is on a white background. There is no evidence in the perception of the test strip for the color complementary to the background. More remarkably, we have found that when a gradient test strip is placed on a background of a different color, the strip is still bleached, and there is still no appearance on the test strip of the color complementary to the background (there is mild uniformspreading or assimilation of the background color onto the test patch). These effects demonstrate there must be some mechanism “removing” color from one area upon contrast with a background area.