Chroma is the measure of color's purity, intensity, or saturation. It describes how vivid or dull a color appears. High-chroma colors are at their most vivid and pure state, meaning they're as intense as they can get without any alterations.

You can decrease the intensity of a hue by adding gray, which reduces its chroma and makes the color less vivid. As you add more gray, the color becomes duller. Eventually, if you keep adding gray, the color will lose all of its intensity and become pure gray. This happens at 0% saturation, where the hue no longer shows its original color.

Another way to reduce chroma is by adding a hue’s complementary color. For example, red and cyan are complementary colors. If you add cyan to red, the red becomes less intense and grayer. When you mix equal amounts of red and cyan, they cancel each other out, leaving no trace of either color. Instead, you get a neutral gray.