I think the colours are mostly open to interpretation, however I suspect I'm part of the reason for the focus on browns; I said before that I like deep rich brown colours. I like the colour anyway, but I also happen to think it's appropriate for us: it's strong, rich and earthy - solid and no-nonsense, which is really what I think we're like as a project and as people given half a chance.
Blue then just comes up at the natural complement (I know orange is the natural complement to blue but somehow the blue/brown combination has worked fairly well IMO)
Personally, I'd be all set with some of the examples posted especially in the last day or so using the blue/brown semi-abstract shapes, but I'm certainly not going to stand in the way of people trying out things.