Color Blindness 2: A world with two hues

One of the more profound discoveries I’ve made regarding color blindness is that there are only two hues in a color blind person’s world: blue and yellow. For some reason I thought that the hues between blue and green were still vivid colors, like this:

But actually it looks like this (deuteranope simulation):

You can see here that turquoise looks the same as gray/white — in other words, it looks colorless. There are really only two hues: anything between them looks less intense, more gray.

White light is a mixture of all colors – it activates all receptors equally. Because turquoise is right between the two receptors it also activates them equally. The two types of light are providing the same information, it takes a third receptor with a different response to tell the difference. Having a third receptor has a profound effect: all wavelengths become distinct colors, a rainbow of hues is visible. Would adding a fourth receptor have a similarly profound effect? I don’t think so — the spectrum is a linear one-dimensional type of information — but maybe I’m lacking imagination here.

Green traffic lights actually have a bluish tinge to them to distinguish them from the red and yellow lights. Because of this, they actually look white! Here is a digitally merged photo I took, along with a deuteranope simulation:

This colorless white/gray effect for hues that hit both receptors evenly is also visible on the other side of the color wheel, in the “unnatural” hues formed by mixing red and blue.

Thus the colors potentially confused by red-green color blind fellows goes beyond distinguishing between hues in the red-to-green range. Turquoise and magenta can be confused for gray, and purple can look blue. I’ll close here with a series of potential color confusions:

One thought on “Color Blindness 2: A world with two hues

  1. KaitlynPonce


    My name is Kaitlyn Ponce’ and I am a student at Walnut High school, CA. For my biology class, we are doing a project on genetic disorders. I was wondering if you could send me some information on Color Blindness. My project is due January 6, 2009. I would greatly appreciate if there is any way you could possibly send the information to me before then.

    Thank you very much for your time.

    Kaitlyn Ponce


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