JoePublic - but GC isn't about realism, exactly.  which has been pointed out.  it's about correct.  and all those different monitors and cameras are sRGB.   see my image for an example of sRGB input in linear calculations displayed on an sRGB output (your screen).  that's a color picker blue (0, 20, 140) at 50% opacity (linear divide) overlayed ( linear add) on another square of blue at 50% opacity (linear divide).  in the center the color at 100% opacity. on no screen will the overlap (which is (0, 15, 105)) and the unchanged square be the same color.  (0, 15, 105) isn't a _bad_ color, it's the wrong color, and not by a little.