http://www.sciencebase.com/science-blog/...romat.html
EXCERPT: [...] There’s a “spectrum” looking chart of different colourful shades, hues doing the rounds now. If you see fewer than 20 different hues, the article accompanying it says, you’re probably a dichromat, two cones in the retina of your eye or one of the three not functioning in the way it should. If you see between 20 and 32 you’re a trichromat, three fully functioning cones. But, if you see 32-39 different colours you have a fourth type of cone in your retina making you a tetrachromat; colours are much more distinguished apparently, but they’re not so keen on yellow. If you can see more than 39 colours, you’re not a pentachromat, you’re a little fibber....
EXCERPT: [...] There’s a “spectrum” looking chart of different colourful shades, hues doing the rounds now. If you see fewer than 20 different hues, the article accompanying it says, you’re probably a dichromat, two cones in the retina of your eye or one of the three not functioning in the way it should. If you see between 20 and 32 you’re a trichromat, three fully functioning cones. But, if you see 32-39 different colours you have a fourth type of cone in your retina making you a tetrachromat; colours are much more distinguished apparently, but they’re not so keen on yellow. If you can see more than 39 colours, you’re not a pentachromat, you’re a little fibber....