Color can be described as having three dimensions: Hue, Saturation, and Brightness.
Hue refers to the color quality and is best described by the names we give colors, like "red" and "green".
Saturation is the purity of the color.
A stimulus of a single wavelength is the purest color;
adding more wavelengths, like adding white to a color, makes the color less saturated.
Brightness is how intense or dim we experience the color.
Trichromatic theory explains color vision by our having three classes of cones
each sensitive to different wavelengths: short, middle and long.
Trichromatic theory helps us explain what we call color blindness.
Most people that we call color blind are not color blind but are missing one of the three cone classes.
Opponent-process theory explains color as the result of different processes
where pairs of colors tend to cancel each other out: red-green, and blue-yellow.
Opponent–process theory helps us understand the color afterimages we see -
for example, seeing a blue afterimage after staring at a yellow patch.