The wheel is a map
Hue is circular: 0° and 360° are the same red. That is why relationships are described as angles — 180° is the opposite color, 30° away is a near neighbour. Saturation and lightness are separate axes, which is why a wheel alone is not enough to describe a color.
The main harmonies
- Complementary — opposite hues (180°): strongest contrast, good for accents and calls to action.
- Analogous — neighbours (within ~30°): calm and cohesive, good for backgrounds and large surfaces.
- Triadic — three hues 120° apart: balanced variety without a dominant pair.
- Split-complementary — a hue plus the two either side of its complement (150° and 210°): contrast with less vibration.
- Monochromatic — one hue at different lightness and saturation: depth without introducing a new hue.
Contrast is not the same as harmony
Harmony decides which hues go together; contrast decides whether text is readable. A harmonious palette can still fail accessibility, so always check the contrast ratio of text against its background — aim for 4.5:1 for body text.
A practical method
Pick one dominant hue and a neutral (near-black, near-white, grey). Add a complementary accent for actions. Keep the accent's area small so it reads as a highlight rather than a second theme. Generate the shades you need from the dominant hue by varying lightness rather than inventing new colors.