Red Green Blue = R G B colour model
A colour model is a model describing the way colours can be represented by numbers, typically as three or four values or colour components. When this model is associated with a precise description of how the components are to be interpreted the resulting set of colours is called a colour model.
The RGB colour model is an additive colour model based on light emitting media such as computer and TV screens or any electric light source in which red, green, and blue light are added together in various ways to reproduce a broad array of colours. Combining one of these additive primary colours with another in equal amounts produces the secondary colours cyan, magenta, and yellow. Combining all three primary colours produces white whereas the absence of any rgb light emitting source is black.
The RGB colour model is the most common way to encode coloured light. Its main characteristic is the quantification of the possible values per component by using only integer numbers within the range of 0 to 255. In this range of 255 red, 255 green and 255 blue values the palette of 16 million colours (255 x 255 x 255) known from computer and TV screens is defined.
This leads to the following description
red green blue
BLACK 000 000 000
WHITE 255 255 255
RED 255 000 000
GREEN 000 255 000
BLUE 000 000 255
Cyan 000 255 255
Magenta 255 000 255
Yellow 255 255 000
This is why colour television or colour computer monitors need only to produce mixtures of red, green and blue light, from where names such as Trinitron besides others are derived.
The additive colour model is in opposition to subtractive colour systems such as the CMYK printing model or the red, blue and yellow one of painting. A subtractive colour model explains the mixing of paints, dyes, inks, and natural colorants to create a range of colours, where each of such colours is caused by the mixture absorbing some wavelengths of light and reflecting others. The main difference in between the additive and subtractive model lies in the manner to produce any colour for example: the mixing of the primary colours in an additive colour model results in white whereas in the subtractive model becomes grey or black. In the same manner yellow being a primary colour in painting in light yellow is achieved by adding red and green light.
As such the RGB colour model describes the fundamental rules of colour mixing within light-emitting devices as opposed to painting or printed media.