Primary Colors Are Red, Yellow and Blue, Right? Not Exactly

Primary colors are fundamental colors that serve as the foundation for creating all other colors in the visible spectrum. You likely learned that red, yellow and blue are the primary colors. You also may have learned of their relationship to other colors.

Secondary Colors

Secondary colors are colors created by mixing two primary colors in equal parts. In traditional color theory, the secondary colors are green (yellow + blue), orange (red + yellow), and purple (red + blue).

Tertiary Colors

Tertiary colors are a mix of a primary color with a neighboring secondary color, resulting in hues like red-orange, yellow-green, and blue-purple.

If you're talking about painting, then yes: Red, yellow and blue are the primary colors. If you're talking about physics and light, though, your primary colors are red, green and blue.

The reason for the confusing contradiction is that there are two different color theories: one for colored light, and one for the "material colors" like the ones painters use or the ones you'll see on a color wheel. These two theories are known as additive and subtractive color systems.

Differentiating Between Additive and Subtractive Colors

Stephen Westland, Professor of Colour Science at the University of Leeds in England breaks things down into simple terms, in an email. "We see because light enters our eyes," he says. "Light enters our eyes in two ways: (1) directly from a light source; and (2) reflected from an object. This leads to two types of colour mixing, additive and subtractive." [We have retained the British spelling of the word "colour" here.]

"Both systems are accomplishing one task," says Mark Fairchild, professor and director of the Program of Color Science/Munsell Color Science Laboratory at Rochester Institute of Technology in New York.

"That is to modulate the responses of the three types of cone photoreceptors in our eyes. Those are roughly sensitive to red, green and blue light. The additive primaries do this very directly by controlling the amounts of red, green and blue light that we see and therefore almost directly map to the visual responses. The subtractive primaries also modulate red, green and blue light, but a little less directly."

First, let's talk about the additive system. When Isaac Newton was 23 years old, he made a revolutionary discovery: By using prisms and mirrors, he could combine the red, green and blue (RGB) regions of a reflected rainbow to create white light. Newton deemed that trio the "primary" colors since they were the basic ingredients needed to create clear white light.

"Additive colors are those which make more light when they are mixed together," says Richard Raiselis, Associate Professor of Art at Boston University School of Visual Arts.

"A simple way to think about additive light is to imagine three flashlights projecting individual circles of light onto a wall. The shared intersection of two flashlight circles is brighter than either of the circles, and the third flashlight circle intersection will be brighter still. With each mix, we add lightness, therefore we call this kind of mixture additive light."

According to Raiselis, imagining each flashlight is fitted with a transparent color filter — one red, one green and one blue — is the key to understanding additive color mixing.

"When the blue flashlight circle intersects the green one, there is a lighter blue-green shape," he says. (Spoiler: We're about to get into secondary colors!)

"It's cyan. The red and blue mix is lighter too, a beautiful magenta. And the red and green also make a lighter color — and a surprise to nearly everyone who sees it — yellow! So red, green and blue are additive primaries because they can make all other colors, even yellow. When mixed together, red, green and blue lights make white light. Your computer screen and TV work this way."

But the range — or gamut — of colors that the three additive primaries can produce varies depending upon what the primaries are. Most sources will tell you red, green and blue are the additive primaries, as Newton originally proposed, but Westland says it's a lot more complicated than that.

"It is often mistakenly written that RGB are optimal because the visual system has receptors in the eye that respond optimally to red, green and blue light but this is a misconception," he says. "The long-wavelength sensitive cone, for example, has peak sensitivity in the yellow-green part of the spectrum, not the red part."

Enter subtractive color. "Subtractive colour mixing results when we mix together paints or inks," Westland says. "It relates to all of the colours we see of non-emissive objects, such as textiles, paints, plastics, inks, etc. These materials are seen because they reflect the incident light that falls upon them."

A piece of white paper, for example, reflects all visible wavelengths. When yellow ink is added to the paper, it absorbs the blue wavelengths, subtracting them from the reflected light. This results in the perception of yellow because the paper now reflects the remaining non-absorbed wavelengths.

In subtractive color mixing, colors start with all wavelengths (white) and then subtract specific wavelengths as primaries are added, contrary to the additive color process.

So the distinction in color systems really comes down to the chemical makeup of the objects involved and how they reflect light. Additive color theory is based on objects that emit light, while subtractive deals with material objects like paintings.

"Subtractive colors are those which reflect less light when they are mixed together," says Raiselis. "When artists' paints are mixed together, some light is absorbed, making colors that are darker and duller than the parent colors. Painters' subtractive primary colors are red, yellow and blue. These three hues are called primary because they cannot be made with mixtures of other pigments."

So, Crayola and Google aren't wrong — in the material world, red, blue and yellow are the primary colors that can be combined to create additional colors of the rainbow.

But if you're talking about anything tech-related (as most of us are these days), remember that the primary colors for TVs, computer screens, mobile devices and more, all subscribe to Newton's light-emitting color system, so their primary colors are red, green and blue. Kind of. Well, not really.

Psychological primaries refer to the basic colors that our brain naturally identifies and processes as distinct. In many cases, these primary colors are red, yellow, green, and blue. Unlike the primary colors used in art or color theory (like red, blue and yellow for paint or red, green and blue for screens), psychological primaries are about how the brain perceives and categorizes color at a fundamental level.

Now it's time for a major primary color revelation. Take it away, Westland.

"It turns out that if we use three primaries, the best ones to use are cyan, magenta and yellow," Westland says. "Note that these are the primaries that have been identified by the large printing companies who will use CMY (and often black as well) in their commercial devices to make a large range of colors. The idea that the subtractive primaries are red, yellow and blue (RYB) is confusing and should not be taught. It would be wrong to think that cyan and magenta are just fancy names for blue and red."

It's shocking, but true: The names we've been using for our primary colors when it comes to paint chips? Totally wrong.

"The subtractive primaries are really cyan, magenta and yellow," Fairchild says. "The names 'blue' for the 'cyan' and 'red' for the 'magenta' are typically misnomers. Other colors can be used as primaries, but they will not produce as wide a range of color mixtures."

The reason behind these inaccurate terms? Light.

"The yellow primary controls the amount of blue light reaching our eyes," Fairchild says. "A small amount of yellow primary removes a small amount of blue light from the original white stimulus (e.g. white paper in printing or a white canvas), while a larger amount of yellow light removes more blue light. The magenta primary controls the amount of green light and, finally, the cyan primary controls the amount of red light. The subtractive primaries do this by absorbing different amounts of red, green and blue, while the additive primaries simply emit different amounts."

It's all about controlling the amounts of red, green and blue light.

What's the Deal With This Misconception?

Westland offers a scholastic example to illustrate the rampant misconception around primaries. "Imagine you are teaching colour science at school and you explain that the additive primaries are RGB and that the subtractive primaries are RYB," he says. "A particularly bright student asks you: 'Why are two of the primaries the same in both systems (R and B) but the G in the additive system is replaced by the Y in the subtractive system?' This is a horrible question because it has no rational answer."

To put it simply, the reason for the lack of rationale is that, as we've discussed, red, yellow and blue aren't the real subtractive primaries at all — magenta, yellow and cyan are.

Teaching About the Relationship Between Primaries

"It turns out that RYB is in fact a particularly poor choice of subtractive primaries," Westland says. "Many of the mixtures that are produced are dull and desaturated and consequently, the gamut of colours you can produce will be small. What you should teach is that there is a clear relationship between the additive and subtractive colour primaries.

"The optimal additive primaries are RGB. The optimal subtractive primaries are cyan (which is red absorbing), magenta (which is green absorbing), and yellow (which is blue absorbing). Now, there is no conflict between the two systems and, in fact, it can be seen that additive and subtractive primaries are almost mirror images of each other. The best subtractive primaries are CMY because the best additive primaries are RGB."

So, if cyan, magenta and yellow are the real primaries when it comes to tactile objects, why does just about everyone on the planet still think the honor belongs to red, blue and yellow?

"Well, partly because they are incorrectly taught this from their first days at school," Westland says. "But also because it seems intuitive. It seems intuitive because people believe the following: 1) That it is possible to make all colours by mixing together three primaries, and 2) That the primaries are pure colours that cannot be made by mixing other colours."

Wait, those beliefs are wrong?

Well, yes, according to Westland, the idea that three pure primaries can create all the colors in the world is totally false. "We cannot make all colours from three primaries, no matter how carefully we choose the primaries," he says. "We cannot do it with additive colour mixing, and we cannot do it with subtractive colour mixing. If we use three primaries, we can make all the hues, but we cannot make all the colours; we will always struggle to make really saturated (vivid) colours."

Even though we're taught to think of red and blue as "pure" colors, they're simply not. Here's how to prove that: Open an art program on your computer and create a red patch on the screen. Then print the patch using a CMYK printer.

"The printer will produce red by mixing the magenta and yellow inks that it has," Westland says. "Red can be made by mixing together magenta and yellow. If we use RYB or CMY — or, indeed, almost any other sensible set of three primaries, obviously not three reds! — then we can make all hues; however, we cannot make all the colors. But we will get the biggest gamut of colours using CMY and that is why we can say that CMY are the optimal subtractive primaries just as RGB are the optimal additive primaries."

And as far as blue goes, it's not as pure as you think either. "It looks pure because it absorbs strongly in two thirds of the spectrum," Westland says. "It absorbs in the green and red parts. Red absorbs in the blue and green parts. If we mix them together, between them they are absorbing everywhere!

"The resultant mixture, although it may be a purple colour, will be dull and dark. The absorption spectra of these colours are too broad. It is better to use cyan than blue because cyan absorbs mainly in the red part of the spectrum; and magenta absorbs mainly in the green part of the spectrum. If we add magenta and cyan together we get absorbing in the red and green parts of the spectrum but we allow the blue light to be reflected."

To break it down, Westland offers this handy guide:

B = M + C

G = C + Y

R = Y + M

If this in-depth explanation busted every color myth that's been ingrained in your brain since childhood and you're feeling a bit panicked, take heart: Coloring books are reportedly great stress busters.

And if you're desperate to learn more, check out Westland's two-minute video series on the subject and his blog. Fairchild also created a great resource for kids, but every adult should be required to study it.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.