Ishihara Colour Test T-Shirt

The Ishihara Colour Test is an example of a colour perception test for red-green colour deficiencies. It was named after its designer, Dr. Shinobu Ishihara, a professor at the University of Tokyo, who first published his tests in 1917. The test consists of a number of coloured plates, called Ishihara plates, each of which contains a circle of dots appearing randomised in colour and size. Within the pattern are dots which form a number or shape clearly visible to those with normal colour vision, and invisible, or difficult to see, to those with a red-green colour vision defect, or the other way around. The full test consists of 38 plates, but the existence of a deficiency is usually clear after a few plates. There is also the smaller test consisting only 24 plates. Answer: 74