An intermediate concept between the key color for a UI theme, and a full
color scheme. 5 tonal palettes are generated, all except one use the same
hue as the key color, and all vary in chroma.
HCT, hue, chroma, and tone. A color system that provides a perceptually
accurate color measurement system that can also accurately render what
colors will appear as in different lighting environments.
In traditional color spaces, a color can be identified solely by the
observer's measurement of the color. Color appearance models such as CAM16
also use information about the environment where the color was
observed, known as the viewing conditions.