Color: More Than Meets The Eye Part Three: What Makes a Color “Primary”?

This is the third post in a four-part series exploring the fascinating evolution of color theory, language, and perception. In this installment, we take another look at different primary colors in three color models — and why “primary” isn’t as fixed a concept as it seems.

Catch up and stay tuned for upcoming posts in this series:

• Part One: Which Color Wheel Are You On?

• Part Two: Color Names – Why Red Came First (And Cyan Came Later)

• Part Three: What Makes a Color “Primary”? (You’re here!)

• Coming Soon: Color in Culture – How Language Shapes Our Palette

What Makes a Color "Primary"?

Is red really a primary color? The answer might depend on what you’re mixing—and why.

We’ve all been taught from our first box of crayons that the “primary colors” are red, yellow, and blue. Mix them in different amounts, we were told, and you can create every other color in the rainbow. But as with many “simple truths” from childhood, the reality is far more fascinating.

What Does Primary Really Mean?

At its core, a primary color is defined as one that cannot be created by mixing other colors within a given system. These primaries serve as the foundation for creating all other hues in that system through various combinations.

But here’s the catch, as we've explored before: there isn’t just one system. Which colors count as “primary” depends entirely on whether you’re working with paint, light, or something in between.

Each wheel tells its own unique story of blending and harmony.

Three Different Models, Three Different Answers

RYB (Red, Yellow, Blue): This is the classic model you likely learned in art class. It works reasonably well for traditional pigments, especially in children’s paints and early art instruction. But, it has limitations as a lot of us have discovered: mixing red and blue gives a muddy purple rather than a vibrant violet. That’s because the pigments don’t behave ideally.

RGB (Red, Green, Blue): On your computer screen, there’s no paint—just light. Screens mix light using the additive model, where the absence of light is black and the combination of all colors is white. Here, the primaries are red, green, and blue because they correspond to the three types of cone cells in our eyes.

CMYK (Cyan, Magenta, Yellow, Black): Printers use the subtractive model, starting with white paper and subtracting wavelengths with inks. Cyan, magenta, and yellow are far more efficient than red, yellow, and blue for producing a wide range of colors. Black is added (the “K”) to deepen shadows and save ink.

The Myth of the Universal Primary

The idea that “red, yellow, and blue” are the universal primaries is more tradition than science. Modern color theory—and the experience of many artists—shows that cyan, magenta, and yellow make a far broader range of vibrant hues. Many contemporary painters quietly swap their reds and blues for these pigment primaries, whether they know the theory or not.

It took me just over 2.5 hours to draw this in Procreate. The human eye is very complex. My illustration only shows some of the components of the eye, as well as a "zoomed in" section of the retina.

The Science Behind Our Vision

Why does the RGB model work so well for screens? The answer lies in biology. Humans have three types of cone cells in our eyes, each sensitive to different parts of the spectrum—roughly red, green, and blue. Our brains mix these signals to perceive the full range of colors. Different species, with different numbers of cones, would have entirely different “primary” experiences of color.

A Personal Reflection

Growing up, I held to the idea that red, yellow, and blue were sacred—unchangeable building blocks of art. I remember the frustration of mixing “purple” and getting something closer to mud.

Years later, I learned about the RGB and CMYK color models, and suddenly the world of color opened up for me. My color mixing became less muddy and so much more vibrant.. It reminded me that even in art, our “rules” are only starting points. The real magic happens when we dare to question them.

Maybe that’s what being an artist is about—experimenting, breaking habits, and finding your own set of primaries.

If You Could Redesign the Primaries…

Primaries are not universal—they are tools shaped by context, whether it’s pigment chemistry, printing technology, or the biology of our own eyes.

So here’s my question to you: If you could redesign the primary colors from scratch, what would you choose? Would you stay with tradition, lean into the science, or invent something entirely new?

Next in the Series: Color: More Than Meets The Eye

In Part Four, we’ll examine how different cultures classify, name, and prioritize colors—and how language shapes what we see.

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Further Reading & Resources

•  The Dimensions of Colour by David Briggs – a deep dive into modern color science for artists.

•  Color: A Natural History of the Palette by Victoria Finlay – a beautifully written exploration of pigments and their histories.

•  Why RGB Isn’t What You Think – MinutePhysics on YouTube – a quick, fascinating explanation of light and perception.

•  Interaction of Color by Josef Albers – a classic text on how we see and use color.