My dads new CLS is Obsidian Black and looks stunning, definately better than the silver. I didn't think it would look too good but once you see it in the flesh it is the nuts
It's so long since I was in school that I've thrown away the slates on which I scratched my notes. The following is the first line of the Wikipedia entry for white: "White is the combination of all the colors of the visible light spectrum".
That might well make you right as the visible light spectrum contains more than just the primary colours.
You're talking about light, not paint! Paint reflects light back of a certain colour, mix enough pigment together and it reflects none back, so it looks black.
Meanwhile I'm undecided about the CLS, it is a colour-sensitive shape and I'm inclined to think that black with grey is a good combination. If it were me buying, I'd consider green-black as it looks black most of the time but when the sun shines it takes on a green/blue/purple tint.