Color in computer vision is most commonly represented as red, green, blue (RGB) values. However, there are many other representations as well.
In physics, color is determined by the wavelength, where visible light ranges from 700nm (red) to 400nm (purple). We can then imagine a light reflecting off an object as a distribution over wavelengths where the mean is the hue, variance is saturation, and area is brightness.
Alternatively, we can represent color as a combination of three bases. Additive components (as with light) are RGB. Subtractive components (as with ink) are cyan, magenta, yellow (CMY).
In this sense, we can think of a specific color as a point within some 3-dimensional cube. A 2D projection of this cube (shown below) then reveals the components mentioned above: RGB are three opposing corners, CMY are another three opposing colors, and white and black are the final two corners. Rotating around the cube changes our hue, moving towards or away from the center changes saturation, and moving into or outward changes brightness.
