You have now met three sets of primary colors. None of them is the one true set; each fits a different medium.
| Set | Primaries | Used for | Mixing |
|---|---|---|---|
| RYB | red, yellow, blue | traditional painting and art classes; the painter's wheel | subtractive |
| CMY (+K) | cyan, magenta, yellow, plus black (K) | printing inks; many modern paint palettes | subtractive |
| RGB | red, green, blue | screens, stage lights, anything that gives off light | additive |
Key idea
Painters traditionally use RYB; printers use CMY plus black; screens and lights use RGB. Each set fits its medium and its kind of mixing.
Why it works
Pigments and inks subtract, so their primaries must be colors that each absorb about a third of the spectrum. Cyan, magenta and yellow do that well, so printers settled on them: together they mix a wider range than red, yellow and blue. Lights add, so their primaries are the three that best stir our three kinds of cones: red, green and blue. RYB remains a useful, traditional teaching wheel.
Piet Mondrian's grid paintings of about 1930 use the painter's primaries, red, yellow and blue, with black lines and white.
Worked example: Which primaries?
A designer makes a poster on a laptop and then sends it to a print shop. Which set of primaries makes the colors on the laptop, and which makes them on paper?
- The laptop screen gives off light: RGB.
- The print shop puts ink on paper: CMY plus black.
Answer: RGB on the screen; CMYK on paper.
Common mistake
Thinking there is one true set of primaries and the others are wrong. Each set is right for its job. The questions to ask: is the color made with light or with pigment, and what tradition is the artist working in?
Why the K? Cyan, magenta and yellow inks together make a muddy dark brown, not a true black, and three heavy layers use a lot of ink. A fourth ink, black, gives crisp text and deep darks for less ink. Printers call it K, for "key."