In my opinion, everything looks so flat and basic. Create something that stands out (or, which is even better, make the whole website stand out) and add it to your web interface. It really does not
need more color, that'd just kill the whole idea of the design. Also, the green and red lines around the boxes doesn't make the design more attractive - perhaps you could make them both a darker shade of gray. Regarding the banner; it's alright, but why make it go further than the actual layout does? If you do this, it's better to not add a border to your banner, so it simply follows the background of the page (if you understand what I mean). The key to make this design better is depth
I hope you can do something with this (and that you don't think I'm just being negative for 'fun'). PS:
You needed something new to add? Try a footer!