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The Ishihara color test is a test for red-green color deficiencies. It was named after its designer, Dr. Shinobu Ishihara (1879-1963), a professor at the University of Tokyo, who first published his tests in 1917.
It consists of a number of colored plates, each of which contains a circle made of many different sized dots of slightly different colors, spread in a random manner. Within the dot pattern, and differentiated only by color, is a number. What, or even if, a number is visible indicates if and what form of color blindness the viewer has. The full test consists of thirty-eight plates, but the existence of a deficiency is usually clear after no more than four plates.
Common plates include a circle of dots in shades of green and light blues with a figure differentiated in shades of brown or a circle of dots in shades of red, orange and yellow with a figure in shades of green; the first testing for protanopia and the second for deuteranopia.
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"Ishihara color test"