(Tye 2006) presents us with the following scenario: John and Jane are both stan- dard human visual perceivers (according to the Ishihara test or the Farnsworth test, for example) viewing the same surface of Munsell chip 527 in standard conditions of visual observation. The surface of the chip looks “true blue” to John (i.e., it looks blue not tinged with any other colour to John), and blue tinged with green to Jane.¹ Tye then in effect poses a multiple choice question.

Most men and nearly all women have non-defective colour vision, as measured by standard colour tests such as those of Ishihara and Farns- worth. But people vary, according to gender, race and age in their per- formance in matching experiments. For example, when subjects are shown a screen, one half of which is lit by a mixture of red and green lights and the other by yellow or orange light, and they are asked to ad- just the mixture of lights (...) so as to make the two halves of the screen match in colour, they disagree about the location of the match. Where one male subject sees the two sides of the screen as being the same in colour, an- other female subject may see one side as a little redder or greener. And there are corresponding differences with age and race. (shrink)