Are Red, Yellow, and Blue Truly the Primary Colors? Think Again

If you ask Google — the ultimate source of knowledge — to identify the primary colors, it will confirm what you learned as a child: red, yellow, and blue. But is that the full story?

Despite the simplicity of this concept, the truth is far more intricate. Google’s answer isn’t wrong, but it doesn’t capture the complete picture either.

The Primary Colors, as You Likely Know Them

Primary colors are the essential building blocks for all other colors in the visible spectrum. Most of us were taught that red, yellow, and blue are the primary colors, along with their connections to other hues.

Colors Formed by Mixing

Secondary colors result from blending two primary colors equally. According to traditional color theory, these include green (yellow + blue), orange (red + yellow), and purple (red + blue).

Intermediate Colors

Tertiary colors are created by blending a primary color with an adjacent secondary color, producing shades such as red-orange, yellow-green, and blue-purple.

Two Color Theories: Additive and Subtractive Colors

In the context of painting, red, yellow, and blue are indeed the primary colors. However, in physics and light, the primary colors shift to red, green, and blue.

This apparent contradiction arises from two distinct color theories: one for light and another for physical materials, such as paints or color wheels. These are referred to as additive and subtractive color systems.

Understanding Additive vs. Subtractive Color Systems

Stephen Westland, Professor of Colour Science at the University of Leeds in England, simplifies the concept in an email: "We see because light enters our eyes. This happens in two ways: (1) directly from a light source, and (2) reflected off an object. This results in two types of color mixing: additive and subtractive." [Note: British spelling of "colour" is retained.]

"Both systems serve the same purpose," explains Mark Fairchild, professor and director of the Program of Color Science/Munsell Color Science Laboratory at Rochester Institute of Technology in New York.

"They modulate the responses of the three types of cone photoreceptors in our eyes, which are roughly sensitive to red, green, and blue light. Additive primaries achieve this directly by controlling the amounts of red, green, and blue light we perceive, closely aligning with visual responses. Subtractive primaries also influence red, green, and blue light but in a less direct manner."

Additive Color Mixing

Let’s start with the additive system. At 23, Isaac Newton made a groundbreaking discovery: using prisms and mirrors, he could combine red, green, and blue (RGB) regions of a reflected rainbow to produce white light. Newton identified these as the "primary" colors, as they were essential for creating pure white light.

"Additive colors are those that increase brightness when combined," explains Richard Raiselis, Associate Professor of Art at Boston University School of Visual Arts.

"To visualize additive light, picture three flashlights each casting a circle of light on a wall. Where two circles overlap, the light is brighter than either circle alone, and where all three intersect, the brightness increases further. Each combination adds more light, which is why this method is called additive light mixing."

Raiselis suggests envisioning each flashlight equipped with a colored filter — red, green, and blue — to grasp the concept of additive color mixing.

"When the blue and green flashlight circles overlap, they create a lighter blue-green hue," he explains. (Hint: We’re diving into secondary colors next!)

"That’s cyan. The mix of red and blue produces a lighter shade, a vibrant magenta. Similarly, red and green combine to form a lighter color — often surprising many — yellow! Thus, red, green, and blue are additive primaries because they can generate all other colors, including yellow. When blended, these three lights produce white light. This is how your computer screen and TV operate."

However, the range — or gamut — of colors achievable with the three additive primaries depends on the specific primaries used. While most sources cite red, green, and blue as the additive primaries, as Newton suggested, Westland notes the reality is far more complex.

"It’s a common misconception that RGB is optimal because the eye’s receptors respond best to red, green, and blue light. This isn’t accurate," he clarifies. "For instance, the long-wavelength sensitive cone peaks in the yellow-green spectrum, not red."

Subtractive Color Mixing

Now, let’s explore subtractive color. "Subtractive color mixing occurs when we combine paints or inks," explains Westland. "It applies to all colors we perceive in non-emissive objects, such as fabrics, paints, plastics, and inks. These materials are visible because they reflect the light that hits them."

For instance, a white sheet of paper reflects all visible wavelengths. Adding yellow ink absorbs the blue wavelengths, removing them from the reflected light. This creates the perception of yellow, as the paper now reflects the remaining wavelengths that weren’t absorbed.

In subtractive color mixing, colors begin with all wavelengths (white) and then remove specific wavelengths as primary colors are added, which is the opposite of the additive color process.

The difference between color systems ultimately depends on the chemical composition of the objects and how they reflect light. Additive color theory applies to light-emitting objects, while subtractive theory pertains to physical materials like paintings.

"Subtractive colors are those that reflect less light when combined," explains Raiselis. "When artists mix paints, some light is absorbed, resulting in darker and duller shades than the original colors. The primary subtractive colors for painters are red, yellow, and blue. These hues are considered primary because they cannot be created by mixing other pigments."

So, Crayola and Google are correct — in the physical world, red, blue, and yellow are the primary colors that can be blended to produce other colors of the rainbow.

However, in the realm of technology (which most of us engage with daily), the primary colors for screens like TVs, computers, and mobile devices follow Newton’s light-based system, using red, green, and blue. Well, sort of. Actually, it’s more nuanced than that.

The Psychological Primaries

Psychological primaries are the fundamental colors our brain inherently recognizes and processes as distinct. Typically, these include red, yellow, green, and blue. Unlike the primary colors in art or color theory (such as red, blue, and yellow for paints or red, green, and blue for screens), psychological primaries focus on how the brain perceives and organizes color at a foundational level.

The Real Primaries

Prepare for a groundbreaking revelation about primary colors. Let’s hear it from Westland.

"It turns out that the most effective primary colors to use are cyan, magenta, and yellow," states Westland. "These are the primaries adopted by major printing companies, which use CMY (and often black) in their commercial devices to produce a wide spectrum of colors. The notion that subtractive primaries are red, yellow, and blue (RYB) is misleading and should no longer be taught. It’s incorrect to assume cyan and magenta are merely elaborate names for blue and red."

Surprising as it may be, it’s true: the primary color names we’ve used for paint chips are completely inaccurate.

"The true subtractive primaries are cyan, magenta, and yellow," Fairchild explains. "Referring to cyan as 'blue' and magenta as 'red' is often incorrect. While other colors can serve as primaries, they won’t achieve the same broad spectrum of color mixtures."

The root of these inaccuracies lies in the behavior of light.

"The yellow primary regulates the amount of blue light reaching our eyes," Fairchild notes. "A small amount of yellow reduces a bit of blue light from the original white source (like white paper or canvas), while more yellow removes more blue light. Similarly, magenta controls green light, and cyan manages red light. Subtractive primaries absorb varying amounts of red, green, and blue, whereas additive primaries emit different levels of these colors."

It all comes down to managing the levels of red, green, and blue light.

Why Does This Misconception Exist?

Westland provides an academic example to highlight the widespread confusion about primary colors. "Imagine teaching color science in school and explaining that the additive primaries are RGB while the subtractive primaries are RYB," he says. "A sharp student might ask: 'Why are two primaries the same in both systems (R and B), but the G in the additive system is replaced by Y in the subtractive system?' This is a tough question because it lacks a logical explanation."

Simply put, the confusion stems from the fact that red, yellow, and blue are not the true subtractive primaries — magenta, yellow, and cyan are.

Explaining the Connection Between Primaries

"RYB is actually a poor choice for subtractive primaries," Westland explains. "Many resulting mixtures are dull and lack vibrancy, limiting the range of colors you can create. Instead, teach that there’s a direct relationship between additive and subtractive primaries.

"The ideal additive primaries are RGB. The best subtractive primaries are cyan (which absorbs red), magenta (which absorbs green), and yellow (which absorbs blue). This alignment eliminates any conflict between the two systems, showing that additive and subtractive primaries are essentially mirror images. CMY works best as subtractive primaries because RGB are the optimal additive primaries."

If cyan, magenta, and yellow are the true primaries for physical objects, why does nearly everyone still believe red, blue, and yellow hold that distinction?

"Partly because this misconception is taught from an early age in schools," Westland explains. "But also because it feels intuitive. People assume two things: 1) All colors can be created by mixing three primaries, and 2) Primaries are pure colors that cannot be made by blending others."

Wait, are those assumptions incorrect?

The Truth About Red and Blue

Yes, according to Westland, the belief that three pure primaries can produce every color is entirely false. "No matter how carefully we select the primaries, we cannot create all colors with just three," he states. "This applies to both additive and subtractive color mixing. While three primaries can produce all hues, they cannot achieve all colors, especially highly saturated (vivid) ones."

Despite being taught that red and blue are 'pure' colors, they aren’t. To test this, open a digital art program, create a red patch on the screen, and print it using a CMYK printer.

"The printer will create red by blending magenta and yellow inks," Westland explains. "Red can be produced by mixing magenta and yellow. Whether using RYB, CMY, or any other logical set of three primaries (excluding three reds), we can achieve all hues but not all colors. However, CMY provides the widest color range, making it the optimal choice for subtractive primaries, just as RGB is for additive primaries."

Similarly, blue isn’t as pure as it seems. "It appears pure because it absorbs strongly in two-thirds of the spectrum," Westland notes. "It absorbs green and red light, while red absorbs blue and green. When mixed, they absorb across the entire spectrum.

"The resulting mixture, though possibly purple, will appear dull and dark. This is because their absorption spectra are too broad. Cyan is preferable to blue because it mainly absorbs red light, and magenta absorbs green light. Combining magenta and cyan absorbs red and green light while reflecting blue."

To simplify, Westland provides this useful guide:

B = M + C

G = C + Y

R = Y + M

If this detailed explanation shattered every color myth you’ve believed since childhood and left you feeling overwhelmed, don’t worry: Coloring books are known to be excellent stress relievers.

For those eager to dive deeper, explore Westland’s concise video series on the topic and his blog. Fairchild also offers a fantastic resource designed for kids, but it’s equally essential for adults.