The additive principle only applies to mixing lights of different colours because the combination of two wavelengths creates the sensation of a third colour. This principle mixes various amounts of red, green and blue light to produce other colours. Combining two of these additive primary colours produces the additive secondary colours cyan, magenta and yellow. Combining all three primary colours produces white.
The subtractive system creates colour by subtracting or absorbing certain colour wavelengths while reflecting others back to the viewer.
But let’s get away from the technical. We are surrounded by colour in our daily lives: the clothes we wear, the colour of our car, traffic lights, neon lights, advertising signs etc. Some of us work very closely with colour; painters and decorators for example. And there’s another side to colour: it fades. Your house may need a new coat of paint on its exterior. Not just to make it look smart but to protect it from the elements. Over time the inside will need redecorating or perhaps you just feel like a change of colour. Now some people are very good at DIY. But others are far better off getting the professionals in. It will cost more, but satisfaction comes at a price!