Primary colors are colors that cannot be created by mixing other colors. Which colors count as primary depends on the system. In traditional painting and printing, the primaries are red, yellow, and blue. In additive light, used by screens, they are red, green, and blue. In subtractive printing with CMYK, they are cyan, magenta, and yellow. Each system produces a different range of possible colors.

The confusion trips up beginners. A designer working in RGB for a website uses red, green, and blue light. The same designer preparing a brochure switches to CMYK inks, where cyan, magenta, yellow, and black build the image. The red on screen will not match the red on paper without careful calibration. Understanding which primaries apply to which medium is basic to color management.

Three systems, three sets of primaries

• RYB: traditional art and painting.
• RGB: screens and digital displays.
• CMYK: commercial printing.
• Each system mixes differently and produces different gamuts.

Primary colors are not a fact of nature. They are a convention tied to a specific medium and mixing method.