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For this example, the blue bands from dark to light value makes the gray background look like it has gradual change of values.
Joseph Alber's Interaction of Colors shows different array of colors that is well needed by the modern artists of today. First published in 1971, it contains 150 color plates of screen printing. It is important to really understand what makes the color seem different, because as artist and designers the subtle control over color enables them to know what to bring out and what to diminish.
Picture from,"Color Interactions" ,Percieve http://www.hutchinsoncenter.umaine.edu/perceive/MachBandExt.html, 1/05/2008