Computer Graphics/Color Models
A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components. When this model is associated with a precise description of how the components are to be interpreted (viewing conditions, etc.), the resulting set of colors is called color space.
The RGB Model edit
The RGB model is the most common model of color used in digital devices (the other being CMK for printing, see below). Color digital displays are based on the RGB model of color. In this model, three channels of Red, Green and Blue colors respectively are combined to form a particular color. The total number of possible colors that can be formed in this way is dependent on color depth, which specifies the total number of bits assigned to the three channels. More the number of bits, more the colors that can be made. Typically, each channel is assigned 8 bits, which gives a total of 2^24 (more than 16 million) possible colors. Although historically, displays with lower color depth have been used in applications like games. For movies requiring visual effects (VFX), color depth used can be more than 24. Also, the colors combine in additive manner, as opposed to subtractive combination of paints.
The HSB Model edit
The HSB model is based around three elements, "Hue", "Saturation", and "Brightness" (or Luminosity). Brightness represents how bright the color appears- the intensity of light, Hue stands for the pure color used. In this scheme, hue is represented by an angle in the color wheel. Red is 0 degrees, Green is 120 degrees and Blue is 240 degrees. The other colors derived by combining these colors lie in between these ranges. For example, orange being a combination of red and yellow (red + green), would be close to 30 degrees and yellow itself would be close to 60 degrees. Saturation is the the amount of hue present in color.
The CMK Model edit
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The XYZ Model edit
This standard was set in 1931 by the International Commission on Illumination(CIE).
It is not practically possible to create a perfect spectrum of all possible colors. Having said that, it is possible to get nearly all possible colors using a set of "primary colors". These primary colors are hypothetical. No real primary colors are defined.