Color, Explained

In 1824 the Gobelins tapestry works in Paris had a complaint on its hands: the black wool looked weak, almost reddish. The chemist put in charge of its dyes, Michel-Eugène Chevreul, tested them and found the black was fine. The trouble was the deep blue and violet threads woven beside it. The black only looked wrong because of its neighbors.

Chevreul spent years on that puzzle, and in 1839 he published a book on what he called the simultaneous contrast of colors. Its lesson is the big idea of this piece: a color is never seen alone. Once you get that, you can use color on purpose instead of by luck: on a canvas, a slide, a living-room wall or a phone screen.

Three dials for any color

Your retina has three kinds of cone cells, tuned to short, medium and long wavelengths of light. Their sensitivities overlap a lot, and your brain works out color by comparing how strongly each kind responds. That is why three numbers are enough to describe any color you can see. Artists usually name them like this:

Most beginners think about hue. Most professionals think about value first. Hold that thought; the third demo below is about it.

Light adds, paint subtracts

There are two ways to mix color, and they behave in opposite directions. A screen makes color with light: red, green and blue light added together build toward white. Paint and ink work by absorbing light, so every pigment you add takes something away, and mixtures slide toward a muddy dark. Your printer uses cyan, magenta and yellow (plus black) for exactly this reason.

Screens add light (left); printers and painters subtract it (right). The same "mix two colors" instruction gives opposite results.

The wheel, and the colors that fight

In his Opticks of 1704, Isaac Newton took the band of colors from a prism and bent it into a circle, joining red to violet. Every color wheel since is a descendant of that move. Colors directly across the wheel are called complements. Put them side by side and each makes the other look more intense.

Vincent van Gogh used that on purpose. Of his Night Café (1888), with its blood-red walls and green ceiling and billiard table, he wrote to his brother Theo that he had tried "to express the terrible passions of humanity by means of red and green."

An honest complication: there is more than one wheel. The painter's traditional red-yellow-blue wheel puts green opposite red. The screen wheel above, built from red, green and blue light, puts cyan opposite red. Neither is "the true one." They are maps for different materials, and the demo uses the screen version because you are reading on a screen.

Color harmonies are not laws. They are reliable starting points, the way a chord is a starting point for a song.

Neighbors change everything

Here is Chevreul's discovery in action. A color drifts away from its neighbor: next to yellow, a gray leans bluish; next to blue, the same gray leans yellowish. Next to black it looks pale; next to white it looks dark. The painter and teacher Josef Albers built a whole course on this, published as Interaction of Color in 1963, and he called color "the most relative medium in art."

Value does the heavy lifting

Strip the color out of a photo and it usually still reads perfectly well. That's because your visual system finds edges, faces and depth mostly from light-and-dark contrast. Two colors can be wildly different in hue and nearly identical in value, and then the boundary between them shimmers and goes soft. Designers call it vibration; readers call it a headache.

This is also why accessibility rules for text measure value, not hue. The Web Content Accessibility Guidelines ask for a contrast ratio of at least 4.5 to 1 for normal text and 3 to 1 for large text, on a scale that runs from 1:1 (identical) to 21:1 (black on white).

Warm, cool and what colors "mean"

Reds, oranges and yellows tend to read as warm and near; blues and greens as cool and far. Landscape painters lean on that: distant hills go bluer and paler, a trick covered in this library's piece on perspective. What colors mean, though (mourning, luck, danger, purity) is learned, and it changes from culture to culture and century to century. Treat any chart that says "blue means trust" as marketing folklore, not science.