There are two different colour systems, additive and subtractive.
Women’s by Flossy Flats 000 Pink Ballet Pnk Baby Pink Mijas TwPqadFIn the additive colour system, used for computer screens, the "main colours" are red, green and blue. It starts with a black screen and adds light to the black
In the subtractive colour system, used for printing, the main colours are cyan, magenta and yellow. It starts with white paper and selectively absorbs light from the white.