Colorblind Colors of Confusion

When people hear that you are red-green colorblind, most of them think, that you can not distinguish between red and green. But that is wrong.

Of course, red and green are some of the problem colors when you are suffering from red-green color blindness. But…

  • … some shades of red and green are easily to distinguish,
  • … and many other colors also cause problems.

The following diagrams of the CIE 1931 color space can give you a quite good understanding of which colors are problematic for colorblind people.

Protan Lines

Deutan Lines

Tritan Lines

All colors in the direction of the lines might be hard to differentiate. There are three different diagrams corresponding to the three main color vision deficiencies: protanopia (red-blindness), deuteranopia (green-blindness), and tritanopia (blue-blindness).

Copunctal Point x y
Protan 0.747 0.253
Deutan 1.080 -0.800
Tritan 0.171 0.000

See Wyszecki & Stiles, Color Science (2nd ed.), 1982, Table 1 (5.14.2) p. 464

The lines shown above are called confusion lines and converge at a point which is called the copunctal point. For the three different types of color vision deficiency there are three different copunctal points.

For the two types of red-green color blindness (protanopia and deuteranopia) the main problem area of colors is really in the axis between red and green. And on this side of the color space, the confusion lines are quite the same for both types. This is why they are called red-green color vision deficiency. But on the left side of the diagram you can see that they are quite different confusion lines which show the problem colors.

If you would like to learn more about color matching and confusion lines you might like to read the article Color Matching and Color Discrimination by Joel Pokorny, a very well known researcher in the field of color vision deficiency.

As you can see from the above diagrams, the whole spectrum of colors is some way reduced for colorblind people. It is definitely not only red and green (protanopia/deuteranopia) or blue and yellow (tritanopia) which can not be distinguished.