The Dirty Little Secret of the Color Wheel

Color is something that you deal with constantly in games and any other form of digital art.  There’s an endless amount of trivia on the subject.  I thought I’d ramble a little about an important aspect of color that we didn’t learn in school.

What we were taught all the way from kindergarten to high school was the “red-yellow-blue” color model.  These were often called the “primary colors” and they were usually shown on a color wheel similar to the one at the top of this post.  This model originated somewhere around 1600 and it was very practical and useful.  It was used in printing as early as the 1700s.  Those three colors are good enough, in the sense that they can be mixed to produce just about any other color in the spectrum.

Red and yellow make orange, yellow and blue make green, and so on.  Everyone has seen and heard about this kind of color mixing at some point.  If you’ve ever actually mixed these colors with paint, you’ve probably run into a situation where over-mixing gives you a muddy grayish-brown as shown in the center of the image above.  It’s also common to find that you need to add some white because you threw in a little too much blue or purple and your mix got too dark.  This is a hint as to what’s really going on here.

Mixing paint or any other kind of pigment (ink, for example) is a subtractive process.  The more you add to the mix, the darker the result gets.  The exception to this is when you add white, and the explanation for that is more complicated than you might expect.  I’ll get back to that later.

There is another way that colors can combine, and that is by mixing light.  This is happening all the time, and it’s the reason why we see all those awesome colors all around us.  The light from the sun is roughly white and it gets scattered through the air, reflects off of all kinds of surfaces, and eventually finds its way into our eyes.  Somewhere around 1800, we figured out that human eyes have three different types of receptors that “see” light.  The three colors of light that we can see are not red, yellow, and blue.  They are red, green, and blue.  The red-green-blue, or “RGB,” color wheel looks like this:

Notice that where the colors overlap, the result is actually lighter than the original two colors that combine there.  For example, red and green add to make yellow, which is lighter than either red or green.  Mixing light is an additive process.  The more light (of any color) that you add to the mix, the lighter the result gets.  In fact, if you mix all three colors of light, you get white.

When you’re mixing colors in a digital art program like PhotoShop, this is the color model that you use.  This is how your computer screen and your television display everything to you – as a mix of red, green, and blue.  Yep, that’s why those video cables in the back used to be color-coded that way, and that’s why you hear terminology like “RGB cables” or “RGB monitor,” etc…

OK, so, since some smart guys a few hundred years ago figured out that we really only see red, green, and blue, where does that leave us when we want to mix paint or ink or whatever?  Making red, green, and blue our new primary colors won’t work because mixing those only makes sense when we’re talking about additive mixing.  If you’ve ever painted something and mixed pure red and pure green, you know that it results in a horrible, useless brown/black color.  Why is that?

The reason is that a “pigment” of any kind is actually something that blocks light.  So think about a big blob of pure red paint.  The reason it looks red to your eyes is that the pigment actually absorbs (blocks) blue and green light and reflects red light.  White light comes from the sun or the light bulb in your lamp, hits that blob of red paint, and all the blue and green components of that light get absorbed into the pigment, but the red component gets reflected and your eyes see red.

(Fun fact – the paint actually heats up very slightly as a result of absorbing those components.  This is why black things feel hotter to the touch on a sunny day than white things.  Black things absorb all the different colors of light and white things reflect all the colors, so white things don’t heat up!)

Now, think about a big blob of green paint.  It reflects green light and absorbs red and blue light.  So when you mix that big red blob with that big green blob, you end up with something that absorbs just about everything!  Those two pigments you’ve mixed now absorb red, green, and blue.  That’s why you see a dark color.  Throw in some pure blue and you’ll end up with black or something very close to it.

So, red-green-blue won’t work as our primary paint colors, and we know that red-yellow-blue also aren’t quite right.  The solution is to choose the pigments that only absorb one color component.  This isn’t intuitive, at first, but it makes perfect sense if you think about it.  Look back up at the red-green-blue color wheel diagram.  Adding red and green makes yellow.  Therefore, yellow is just the color you get by reflecting red and green and absorbing blue.  A yellow pigment absorbs only one color: blue.  Adding blue and green (again, we’re mixing light here) gives you cyan.  So cyan is the pigment that reflects blue and green but absorbs only red light.  Finally, adding red and blue makes magenta, meaning that magenta is the pigment that reflects red and blue but absorbs only green light.

It can be confusing because it’s kind of the opposite of what we learned as kids, but you gotta trust me here!  The “real” color wheel is actually this:

The primary colors are cyan, magenta, and yellow.  This is commonly abbreviated as “CMY,” and you’ll see this a lot if you work with any kind of modern printing.  It’s also common to see “CMYK,” where that extra “K” stands for black.  They chose not to use “B” for black because it’s so commonly used to mean “blue.”

So, if you want to paint or print or do anything that involves mixing colors, and you want to know the true primary colors that will mix to give you all the others, they are cyan, magenta, and yellow.  If you don’t believe me, open up your color printer and look what color the ink cartridges are!  Knowing this, it’s not hard to see why red-yellow-blue stuck with us for hundreds of years.  Yellow is correct as a primary color, and cyan is pretty close to a light blue and magenta isn’t far from a light-pinkish red.

One last note.  The concepts of primary, secondary, tertiary (and so on) colors is still perfectly fine.  The catch is just that they aren’t quite the same as you might have learned.  The primaries are cyan, magenta, and yellow; the secondaries are red, green, and blue; and the tertiary colors are things you get by combining those, like orange, yellowish-green, bluish-purple, and so on.

Now go get some Crayola markers and try to prove me wrong!

This post’s header image is from “Chromatography; or, A treatise on colours and pigments: and of their powers in painting,” by George Field, 1841.

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