Color wheel
See how colors relate before you commit them to a page.
Click the wheel to set a base hue. Choose a harmony and watch the related colors lock into place. This is color theory you can steal.
How the wheel works
Primary hues sit 120° apart. Mix two primaries and you get a secondary. Mix a primary with a secondary and you get a tertiary. The wheel is a map of those distances, not a decoration.
Complementary colors are 180° apart. They make each other louder. Analogous colors sit next to each other and behave like a family. Triadic schemes are three equal steps — useful when a scene needs energy without a single screaming accent.
In comics, pick a harmony first, then decide which member of that family is allowed to be loud. A complementary pair with both sides at full saturation will fight the line art.