I think it looks nice and I think the colors are a great choice.
I am not personally a fan of the narrow fixed width,
however I see lots of forums that use the narrow fixed width so apparently this is just a really personal preference that many will disagree with

I just personally think you could be wasting space for useful information or maybe even ways to monetize, eventually. Have you thought about possibly adding a side bar to either side?
Aside from that, I really love the idea and the design (colors, layout, etc). Good job!