Colors are sleek, still I have some suggestions which you might consider next time.
A small border that will devide forum and background is a nice to have, much better If you use CSS3, at least for mozila. Also around categories it's much better with rounded edges. Who's on line image is not neccesary at PHPBB3 skins. I like the icons. I don't like gray boreders, maybe a darker blue is better to fit. Still, I have one more thing to add, you could have added a nav. bar or at least small images next to text, but If you wanted text you should have put a line to devide nav and body.
