We all have three types of color photoreceptive cells in the back of our eyes (the retina) – which are often called the red, green, and blue “cones.” We are trichromats. Each of these ‘flavors’ of cone is sensitive to a particular range of colors of the spectrum. And usually when we perceive a color, it is the result of a combination of signals from more than one flavor of cone. For example, seeing “orange” is the result of a moderate signal from a green cone and a stronger signal from a red cone. And we are able to distinguish the range of orange hues from each other by the different strengths of green and red cone signals that each orange hue generates (darker orange would have a stronger red signal, etc).
Can you see any symbols or letters in these circles?
But how many shades can you see here? Count them!
*If you see more than 33 shades, you are a tetrachromat, like bees, and have 4 types of cones (in the purple/blue, green, red plus yellow area). You are irritated by yellow, so this color will be nowhere to be found in your wardrobe. 25% of the population is tetrachromat.*If you see more than 39 color nuances: come on, you are making up things! There are only 39 different colors in the test and probably only 35 are properly translated by your computer screen anyway :)
But eyes change over time. You may have heard that digital cameras can be by removing the IR filter found inside, but did you now that something similar can be done with the human eye? People who have aphakia, or the absence of the lens on the eye, have reported the ability to see ultraviolet wavelengths. Claude Monet was one such person: