Primary School (Part the Second)

Chalkboard Color 2.png

Welcome back for another installment of tearing down the classic color wheel we all know and love from childhood art classes!

Just kidding, sort of. Today we’ll talk about primary colors in pigment, following up on my last post about primary colors in light. (If that doesn’t sound familiar, check it out or go farther back to read about the history of color perception!)

To understand why primary colors (which can be mixed to create all other colors) are different for light and pigment, we need to know how we see light and pigment differently. By pigment I just mean anything that gives something a visible color, whether it’s plant chlorophyll or oil paint.

How does that work? Well, some objects are sources of light, which shines into our eyes, allowing us to see them. Most things aren’t light sources, though, so we only see them because light bounces or reflects off them. What gives them color is that we only see certain wavelengths of light reflected, meaning that the material is getting hit by a huge range of wavelengths and absorbing a lot of them, only reflecting some. (This could also be because only certain wavelengths hit different objects in the first place, but that’s usually not the case.)

So the main difference between the colors of red light and an extremely red, Snow White-type apple is that red light only has red wavelengths to start with, while the apple greedily gobbles up everything except red wavelengths. What happens if you add another color, though?

Well, if you add blue light to red light, now it’s activating your red cones and your blue cones, and you end up with purplish or magenta light. As a side note, if you’re curious you should read about how we see purple (and violet, which it turns out are different things) as between blue and red, when the color spectrum doesn’t actually cycle back around from blue to red.

Color Additive.png

If Snow White’s stepmother magically adds blue to her red apple, things are a bit different. By itself, the red apple will reflect red light but absorb blue light; now she’s added something that will reflect blue light but absorb red light. Mixed together, these colors will end up absorbing…well, everything. Nothing gets reflected, and the apple turns black, which probably will tip off even the most naive princess that something’s up.

Color Subtractive Black.png

“Black Delicious” is a terrible name for an apple, but on the bright side, it’s at least a more obvious lie than “Red Delicious.”

This is what people mean when they say that light colors are additive (red + blue = magenta) and pigment colors are subtractive (red – blue = black). Basically, for a pigment color to fit the bill of being primary, it’s got to have a wider range of reflected light. Otherwise, things are going to get dark fast because all the light will end up being absorbed when colors are combined.

The sensible answer is to pick colors that each activate two types of cones. (Activating all three gives you white, which is nice but can’t really form other colors.) That way if you combine red- and green-reflecting pigment A with green- and blue- reflecting pigment B, the combination will absorb blue thanks to A and red thanks to B, but it’ll at least still reflect green.

Color Subtractive Green.png

With this requirement in mind, the primary pigment colors end up being yellow (reflecting equal red and green light), cyan (reflecting equal green and blue light), and magenta (reflecting equal red and blue light). These colors will be familiar from printer ink cartridges, which use combinations of the three to print any other colors you want. Generally, graphic designers and printers work with the CMYK (cyan, magenta, yellow, black) color wheel.

Now that we have six colors to work with, we could try redrawing the classic six-color wheel to reflect the primary colors we’ve just talked about.

Color Wheel New.png

Hey, nice! Our primary colors for light and pigment are equally spaced around the circle, and each light color is opposite the pigment color that absorbs it. That actually seems useful.

Another possible color wheel design is based on the psychological primaries, or the red-green and blue-yellow opposites of opponent process theory. I illustrated this idea in my previous post as two axes where colors can’t be both red and green, or both blue and yellow. A color wheel based around those would look more like this, with secondary grades in between that I won’t include because I’m lazy:

Color Wheel Opponent.png

So with all these options, why do we keep teaching kids about red, yellow, and blue and drawing a color wheel with the six (somewhat arbitrary) colors of the rainbow?

First, the RYB (red-yellow-blue) color model is older than either the RGB-based CMYK model or the opponent process model. Red and blue aren’t quite as good for subtractive color mixing as magenta and cyan, but they’ve done well enough for centuries of painters, especially if they’re not purely reflecting only one color. That means they’ve got the huge power of tradition on their side. We tend to teach our children what we were taught ourselves, especially if we feel like we understand that much better than the alternative.

Also, I think the color names are a big factor. Sure, we could replace blue and red with cyan and magenta, but gee, which names are easier to say? Magenta and cyan sound way too fancy to be basic, primary colors. I mean, you don’t even get colors like that until you get into the giant box of crayons! How important can they be?

In the end, the colors do look sort of similar to each other, so maybe using the RYB model in school isn’t the end of the world. On the other hand, I personally would’ve saved a lot of confusion if I’d learned about cyan and magenta as a kid. It would make it so much easier to talk about light and pigment together.

Instead, I learned about CMYK in journalism class, though not why we used them, and then spent years vaguely wondering why paint primaries and light primaries were the same for red and blue but different for the third color. Now I understand it all a lot better after researching these posts, and I hope you do too!

Maybe I’ll be one of those parents someday. You know the ones: “Dr. Bennett, your daughter has been confusing the other kindergarteners by insisting that magenta and cyan are primary colors.” Just wait till she tells them that Santa Claus is just as imaginary as his big old primary-red suit.


I invite, nay, beg you to check out other resources if you want to know more. There are people on the internet (not to mention in books!) who have written at great length without any worries about keeping it brief-ish, which I try to do. If you want more than you could possibly cram into your head about color theory, check out this nearly-endless site. For something only a little longer than this post, try this other blog. Enjoy!


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