I think that the template looks quite nice, you could however probably improve it by making the grey less prominate, perhaps by making the green areas wider/bigger and changing the shades of grey for the main list of boards, which looks really monotone grey.
Expanding on what LHVWB mentioned about the background colors, perhaps you can experiment with a different color for the background that is within the two vertical green bars that define the page. That way, it could look as if the forum is overlaid on top of the gray background? I'm not sure if that made much sense.
You should blacken the user name text/ guest text. the text seems to blend in with the navbar stuff. The buttons up top seem to pop out weirdly to me. Maybe you should put the same text effects like in the logo to the buttons.