UNITED KINGDOM - DECEMBER 18:  Most colour blindness is inherited, and affects more men than women. Colour blindness usually involves confusion between red, green and yellow. Dr Shinobu Ishihara, Professor Emeritus of the University of Tokyo, Japan, designed this series of plates as a test for colour blindness. The test involves the patient being able to distinguish a number within the coloured field at the centre of each chart.  (Photo by SSPL/Getty Images)