Atleast im not the only crazed one out there, Pink Floyd that it is .

Think of the diagram in the colour chart each of the 3 colours overlap in the center, the center is the colour they all make and so the thing they all have in comon is they are needed to make sed colour. Add a 4th colour and you are left with a center colour and 3 outa colours that putting 2 of the 4 colours together will make.
(Have i confused anyone yet? not as dumb as i seam)