Christmas for the Red-Green Color Blind

What would Christmas be like without red and green? No candy canes, Christmas trees, or red-vested Santa?

At this year’s Christmas feast, you know, the one with the ham sandwiches, potato chips, and red-green jello salad, when wondering what to talk about with your know-it-all, nerdy cousin-turned-doctor (cough, cough), or your Uncle Rob and his insisting that all facts be appropriately cited as, “In last Tuesday’s Wall Street Journal…” this article is for you. When conversation becomes bland with your somehow-still-connected-but-very-far-extended family, try out this Christmas quiz question to stump your sister-scholars, confuse your magna-cum-laude cousins, and stimulate some not-so-subtle googling by your gadget-savvy grandpa.

What would Christmas be like for the red-green color blind?

First, some background on color vision:

The human retina contains two types of photoreceptors, rods and cones. Unlike the rods, the cones are sensitive to color, and are highly concentrated in the central, yellow spot of the eye known as the macula. At the center of the macula is a region known as the fovea centralis, a 0.3 mm diameter area made up of very densely-packed cones. The colors you see all around you are composed of different energies and wavelengths, and it is the cones which sense these different wavelengths of light, allowing the brain to translate the wavelengths into the different colors to which you have grown accustomed. In 1802, Thomas Young proposed that color is perceived by three principal color receptors, as opposed to the previous theory which claimed the world’s thousands of colors were perceived by thousands of individual color receptors. The three types of color receptors, or cones, which perceive the different wavelengths of light are S-cones, which sense short wavelengths, M-cones, which sense middle wavelengths, and L-cones, which sense long wavelengths. Individuals that have properly functioning cones of all three types are known as tri-(think three) chromatic. Just as the colors of the rainbow are made up of combinations of three primary colors, individuals that are trichromatic can see all colors in the rainbow because their properly-functioning S-, M-, and L-cones can unmix the visible color combinations into their separate wavelengths and interpret these wavelengths accordingly as colors. Individuals with partial color blindness have a spectrum of retinal cone dysfunction, impairing their ability to perceive differences in color. On the other hand, individuals with monochromacy, such as in complete achromatopsia, see no color at all, and their world consists of different shades of grey ranging from black to white, as if their whole world were an old-fashioned black-and-white movie. These individuals must rely only on their still-functioning rods, as the cones, if present at all, do not function correctly. This condition, however, is very uncommon, affecting only 1 in 33,000 individuals. The vast majority of color-blindness, comprising approximately 8% of the population, is due to dichromacy, where individuals are unable to see a specific section of the color spectrum because their ability to see a specific color hue is limited to mixing only two other wavelengths of light (as opposed to the three wavelengths needed by people with normal color vision).

Okay, let’s get back to Christmas dinner with the relatives and the discussion of red-green color blindness.

Dichromacy, the most common form of color-blindness can be further separated into three categories: protanopia, deuteranopia, and tritanopia.

Individuals with protanopia have a reduced ability to see red, those with deuteranopia have reduced ability to see green, and those with tritanopia have reduced ability to see blue. Due to overlapping sections of the color spectrum perceived by both red and green cones, individuals with protanopia and deuteranopia see a similarly-impaired spectrum of colors, and thus are commonly known as having “red-green color blindness.”

There are, however, important differences between how the red-green color blind protanopes (reduced ability to see red) and red-green color blind deuteranopes (reduced ability to see green) see the world around them.

Protanopes are more likely to confuse:
1. Black with many shades of red
2. Dark brown with dark green, dark orange and dark red
2. Some blues with some reds, purples and dark pinks
3. Mid-greens with some oranges

Deuteranopes are more likely to confuse:
1. Mid-reds with mid-greens
2. Blue-greens with grey and mid-pinks
3. Bright greens with yellows
4. Pale pinks with light grey
5. Mid-reds with mid-brown
6. Light blues with lilac

So how do you know if you are color-blind? Believe it or not, diagnosing color blindness is harder than you might think. Individuals with this ailment rarely complain to their eye doctor that they “cannot see red.” In fact, most people with a form of color-blindness adapt quickly, learning the colors based on what they see rather than what the rest of the world sees. For example, when learning colors as a child, those with protanopia may learn the color red to be the muddy-brown color that you and I see in the picture above. It is often only when asked to differentiate similar colors that individuals first recognize their color blindness. One of the most common tests used for color blindness today was first invented by Dr. Shinobu Ishihara in 1917. Known as the Ishihara plates, this test consists of 24 plates with a dot-shaped pattern inside a circle, forming a number or shape clearly visible to those with normal color vision, and invisible, or difficult to see, to those with a red-green color vision defect. In the image below, individuals with normal color vision see the number 74. Those with red-green color blindness, however, see the number 21. What do you see? Click here to take the full Ishihara color plate test for yourself. Who knows, you might be color-blind!

So now that you are an expert in color blindness, and are ready to take on the keen intellect of your relatives at this year’s Christmas feast, take a look at the image below to see what Christmas might look like for those with red-green color blindness.

In the legendary Christmas book How the Grinch Stole Christmas, Dr. Suess describes how, “The Grinch hated Christmas! The whole Christmas season! Now, please don’t ask why. No one quite knows the reason.”

To Dr. Suess I say, “Maybe, just maybe, the Grinch had good reason for his complete hatred of the whole Christmas season – for the Who’s tree when seen from the rooftop on down, looked to be lacking color, a pale muddy brown!”