Why Are Digital Colors Expressed By RGB And Not The RYB (Primary Colors) Model?

We were taught in school that the primary colors are red, yellow, and blue, and that we can get any other color by mixing these three colors together. Yet as you got older, chances are you noticed colors being represented through a different, broader model: RGB (red, green, and blue). So where did this distinction come from exactly?

To understand the difference between the RGB and RYB models, you must first understand how the "eye" actually sees color, and that primary colors aren't exactly, primary.

The human eye has three different types of cone cells that can each "see" a different color of light. These are roughly red, green, and blue. So, right there, you should be able to understand why colors on a screen are represented by red, green and blue; they're just tuning in to what our eyes can see. By mixing these colors of light, we can create all the other colors our eyes can see.

So why are the so-called primary colors red, blue and yellow?

When people started thinking about colors, they had no idea about how light worked, or how our eyes worked, but we did know something else: paint. Remember that early humans started experimenting with paints since prehistoric times. At some point in history it was discovered that by mixing colors of paint, you can get a different color. By trying a lot of combinations, people found out that with red, blue and yellow, you can make (almost) any other color. Thus, the idea of "primary colors" was born.

But mixing colors works a little different from mixing light. Paint has a certain color, because it absorbs all the other colors. So if you add different colors of paint together, the mixture gets darker (this is called subtractive color). But if you mix different colors of light together, the mixture gets lighter (because more light!). This method of combining colors with light is called additive color.

primary colors representation

Now that we know how light and our eyes work, we have learned that what we first called primary colors are slightly off. To be able to make all different colors using paint, you actually need

  • Yellow (that one was right) - a product of mixing red and green light
  • Cyan (a sort of light blue) - a product of mixing green and blue light
  • Magenta (a sort of pink) - a product of mixing blue and red light
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