The vocabulary behind every color decision.
Color theory isn't a set of rules to memorize — it's a vocabulary for describing what you're already seeing, so you can make deliberate choices instead of guessing.
Primary
Red, yellow, and blue — the three hues that can't be mixed from any others.
Secondary
Orange, green, and purple — each made by mixing two primaries in equal parts.
Tertiary
Six in-between hues, each a primary mixed with its neighboring secondary.
Hue, saturation, lightness
Every color you pick on the wheel has three properties. Hue is the color itself — red, blue, green — and it's what the wheel's angle represents: 0° is red, 120° is green, 240° is blue, and it loops back to red at 360°.
Saturation is how intense or muted a hue is — how far from the center of the wheel you are. Full saturation at the edge is the purest, most vivid version of that hue. Near the center, every hue converges toward gray.
Lightness is how close a color sits to black or white, independent of hue or saturation. A fully saturated red at 10% lightness is a near-black maroon; the same red at 90% lightness is a pale pink. Hue and saturation stay identical — only lightness moves.
Primary, secondary, tertiary
In the traditional (pigment-based) color wheel, red, yellow, and blue are primary — they can't be mixed from other colors. Mixing two primaries in equal parts gives a secondary: red+yellow=orange, yellow+blue=green, blue+red=purple.
Mixing a primary with an adjacent secondary gives a tertiary — red-orange, yellow-orange, yellow-green, blue-green, blue-purple, red-purple. This is the traditional 12-hue wheel most people learned in school. Screens use a different primary set (red, green, blue) for physical reasons covered on the Light vs. Material page.
Warm and cool
Reds, oranges, and yellows read as warm — they advance toward the viewer and are associated with heat, energy, and closeness. Blues, greens, and purples read as cool — they recede, and are associated with calm, distance, and cold.
This isn't just cultural association. Warm colors genuinely appear to sit closer in a composition, which is why painters push backgrounds cooler and foreground subjects warmer to build depth without changing a single value.
Contrast and legibility
Two colors can be visually striking together and still fail as text-on-background — hue difference alone doesn't guarantee readability. What matters for legibility is the contrast ratio between their lightness values, which is why the wheel tool checks your chosen color against pure white and pure black separately and flags whether it passes accessibility guidelines (WCAG AA) at each.