Everybody is Color Blind

Are you colorblind? No, you don’t think so? — I am sure you also have some form of color vision deficiency or colorblind sensations. You don’t believe me? I’ll prove it in the following article.

I would like to show you four types of color blindness which are true for almost all of us. Starting with a very simple form we will definitely get into more details when it comes to small-field tritanopia, which strongly supports my statement that everybody is colorblind.

(A) Colorblind in the Darkness

When it is getting dark at dusk colors start to fade. You start to mix up colors and are not so sure any more when it comes to naming a specific color. So one could say that everybody is colorblind in the darkness.

I know this is not such a strong argument to support my statement, but it is a very good example to get an impression of how it feels like if you would have some form of color vision deficiency.

(B) Ultraviolet and Infrared Blind

Non of us can see both far ends of our color spectrum: infrared and ultraviolet. We name those colors but we can’t see them. This doesn’t necessarily means we are colorblind if nobody can see them anyway. But there are creatures who can see those colors.

A lot of people heard that bees can see ultraviolet light; which is true. But they don’t have a broader color spectrum as they also have only three different color receptors like people with normal color vision. Bees see less reds and more blues, that’s not really better than us isn’t it.

But there are some fish, some turtles and the whole family of birds who can perceive our whole color spectrum and also ultraviolet light. Birds have four different color receptors (tetrachromats) and clearly can see more colors than you and me. On the other side we have for example rattlesnakes which have some form of infrared eyes which can see the prey at night.

(C) Tetrachromacy

If you believe it or not but not only animals are tetrachomats but also humans can have four different color receptors!

Studies have shown that women who carry the color vision defective gene, can develop four different receptors in the eye and therefore have a broader color spectrum than the rest of us. This is a very rarely diagnosed phenomenon but definitely makes all of us colorblind compared to tetrachomatic women.

(D) Small-Field Tritanopia

And if you think the three points above don’t really prove that we are all colorblind this last point will definitely change your mind.

Normal color vision means you have three different color receptors: one peeking at red (L-cones), one at green (M-cones) and one at blue (S-cones). Together we have about 4.5 million of those receptors distributed all over our retina. Most of them are L- and M-cones and only about 7% are blue sensitive.

A closer look at the distribution of the color receptors shows, that in the very center of the retina, inside the fovea, there are no blue cones at all! As this spot is very small—you can think of visual field the size of a tennis ball at the other side of the court—this is called small-field tritanopia. See also my article about tritanopia to learn more about this type of color vision deficiency.

So in the center of our visual field we have no S-cones. This means only L- and M-cones can give us information about the colors in that spot and therefore we are all dichromats in the fovea. — And why do you don’t know anything about your central color blindness? Because your eyes don’t really focus on such a little point but often move around. This makes you believe, that you have trichromatic color vision over your whole visual field.

And because small-field tritanopia is true for all of us, everybody is at least a little bit colorblind! quod erat demonstrandum.

4 responses on “Everybody is Color Blind

  1. Matt Doar

    Excellent!If only some of those chemicals that can change our color vision weren’t toxic, it would be great to be able to simulate colorblindness for a short period of time.

  2. y-thingy

    I didn’t know about the “(D) Small-Field Tritanopia”. Do you have some links explaining this more?

    I have a colorblind son and I was wondering if I could have tetrachromacy. After all sorts of tests I found out he’s got protanopia. I guess I don’t have an extra cone at all. Well I should have know by now that I don’t have super color vision, only normal color vision. :) Oh well.

  3. Dan W.

    I’ve often thought that we are all colour blind since if we were NOT colour blind then rainbows would not appear to have any stripes.

    I presume everybody else sees the same strips that I see. If we were not colour blind, a rainbow would simply be a continuous blend of colours from one end of the spectrum to the other.

    It would be interesting to ask a person with tetrachromat vision to depict a rainbow by drawing outlines of the stripes that they observe.

    I see the ones that I was told to see: ROYGBIV — seven.

    Trichromat vision includes 3 cones which, if they were digital (on/off), could code for 8 colours (2 to the power of 3 — where on/off has two states and there are 3 distinct cones). So it is perhaps no coincidence (really?) that culturally, we speak of 7 colours in a rainbow (how many do various cutures distinguish, I wonder).

    I presume that we speak of only 7 rather than eight because the 3 cones are not perfectly distinct — they overlap — and so we observe fewer than 8 distinct colours

    Using the same thinking, it seems that tetrachromats should observe no more than 16 stripes(2 to the power of 4) in a rainbow.

    Amd now that I’ve taken the anomoloscope I am reflecting on the results (I only matched one), and I realize that the principle that underpins this test might also be used to argue in support the hypothesis that a tetrachromat would ineed see more than 7 (but fewer than 16) stripes in a rainbow.

    But I’ve never heard anybody (first hand or second hand) describe a rainbow with more than 7 stripes. It seems that if such people exist they must be quite rare.