A color is a representation, created by our brain, of waves picked up by specific cells of our retina: cones (three types which detect the presence of three wavelengths corresponding to blue , green and red) and sticks (sensitive to the intensity of light, especially useful for night vision).
There are two ways to define any color using only three primary colors (C1,C2,C3):
• additive color method with RGB coding: a mixture of Red Green and Blue is added to blacK K(0,0,0) Lighting a black video screen.
example: hexadecimal RGB coding of the orange (1, 0.6, 0) = (255, 153, 0) = #ff9900
• subtractive color method with CMY coding: a mixture of cyan, Magenta and Yellow is subtracted from White W(1,1,1) Painting on a white sheet.
Remark: R+C = G+M = B+Y = 1 thus it is easy to switch between the two coding methods (the mixture of two of the three fundamental colors is the complementary color to the third fundamental color).
Exchanging the codings R G B and C M Y exchanges the image and its "negative", thus also black and white (see the cube at the bottom of the page).
A color can also be defined with its hue, its saturation and its brightness (HSB coding).
