The primaries of additive colour (red, green and blue) have become a standard way of organising colour in computer programs.
A way of visualising RGB colour is through a cube. Starting in the black corner we can travel right to the red, vertically to green or back to blue. Mixtures of red, green and blue generate all the colours within the cube. The diagonally opposite corners pair primaries with their complementary colours. The black/white diagonal provides the grey scale.
Back to colour on computers