Conversations on Colorblindness
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Part four of my conversation with

Dennis wrote -

I have found out some interesting things through a friend of mine who is also colorblind. We both see green stop lights as a very white to light green light which I have notice to be true with practically every colorblind person I have met.

We sat down one day and went through the various colorblind tests on the WEB. It is interesting to note we both had the same problems with the eye charts. The ones I could barely see he could also barely see. Then I started to notice that I could see some of the yellow green ones a little better and he could see the reddish ones a little better. He can also distinguish purple from blue with no problem ( I have a problem). He also does not have a problem with the intensity of red lights such as clock LED's and so on. It was the first time I was able to test for duetan (Green) or protan (Red) color deficiency. My friend is definitely a duetan and I am definitely a protan, but we have about the same problem telling colors in the red to green region.

I find this very interesting, its like if the brain is missing either red or green the same result of color perception results. Although I can usually see some green in green stop lights, my friend doesn't see any green at night in green stop lights, just a clear white. My description in the past of asking if all stop colors appear to be of the same intensity I think has to many human judgement factors. My guess (only a guess) is you are color blind like me and are a protan because only protans (like myself) have problems with red on black. The amount of protanomalism (anomalous trichromat) varies from a complete lack of red cones to almost normal amounts. This probably determines how well someone sees red on black. By the way a protan that has only two color vision (no red cones) can't tell chocolate syrup from ketchup or a ripe tomato from a green one. I think from yours and my descriptions, we are far from this level of colorblindness and are like 70% of colorblinds with only modest color deficiency.

Last updated March 5, 2001