The case under consideration was brought to my notice while I was attempting to arrange a colour match by the well-known disc method. The colour was somewhat like lilac, though rather more red. A number of onlookers—including the gentleman whom I afterwards found to be colour-blind, and whom I shall in this paper denote as Mr A.—pronounced the match fairly satisfactory. Mr A. subsequently remarked to me that he sometimes had a difficulty in distinguishing greens and blues. He said, also, that he had, though much less frequently, a difficulty with reds. This condition is so abnormal that I at once handed him a direct vision spectroscope and asked him to name the colours which he saw in succession from one end of the spectrum to the other. He said that red was the first. “And after the red?” I asked; “green,” he said: “and after the green?”; “blue.” And when asked what followed the blue, he said that the rest of the spectrum was blue throughout the whole extent. When asked if he saw white light between the red and green colours, he was very undecided, but said that he did not think he would call it white—it might be yellow.