Let's start with some vsauce:
As you may know, the human eyes contains three types of cones (high, medium, and low), which are used to perceive color. Each type of cone is tuned to receive light of certain wavelengths (high, medium, and low--go figure). We do not need a separate receptor for every color that we see because 3 receptors are enough to triangulate the color of the light entering our eyes.
But what if you have only two receptors?
This is how I used to understand all colorblindness. I thought that either we (the colorblind) had only two types of cones or the third type was weak or inoperable. This does happen and it is called dichromacy.
You might be able to guess that different varieties of colorblindness result from the impairment of different types of cones.
(Note: monochromacy results from only one working cone; this is when someone truly sees in only grayscale. Guess what? There are actually three types of monochromacy, and three corresponding grayscales. I don't think much research has been done on distinguishing these.)
If you remember the picture from the video, the medium and high sensors actually detect relatively close-to-the-same wavelengths of light. A lack of either results in the inability to distinguish RED from GREEN. That's right, two completely different defects can result in red-green colorblindness. Deuteranopia happens to be the most common.
Nevertheless, Protanopia and Deuteranopia are subtly different, as indicated by the following two images from color-blindness.com.
|Protanopia Confusion Lines|
|Deuteranopia Confusion Lines|
Here's the neat part. I (like many "colorblind" people) have three types of perfectly working cones. I am a trichromat. So why can I not see all the colors that most of you can see? Colorblind people such as I have an anomaly in the relative sensitives of our cone types.
Essentially, one or more of the bell curves on the graph up there is shifted to the left or the right. Our eyes triangulate light waves differently and as a result, we cannot distinguish all of the colors/hues that normal trichromats can.
According to a slew of tests that I found online, I have determined that I likely have a certain (common) anomaly in which I more or less have two high-frequency-sensitive cones. The sensitivities are enough different that I can distinguish more colors than a deuteranope, but I still cannot see many of the "normal" colors.
Here's the REALLY neat part. Because of the difference in cone sensitivities, I may actually see colors that normal-vision people cannot see. How cool is that?
Some other neat stuff:
TED Talks: Beau Lotto
Radiolab: Why Isn't the Sky Blue?
Describing Colors to Blind People
Vsauce: perception and qualia