The colors are not bad. They are warm and comfortable.
The header ad is very large. If it is a "must have" so be it, but if it isn't, I'd remove/move it. Maybe an ad on the side would be better? Kind of like that. ==>
Your buttons need a lot of help. You have at least 4 different types throughout your forum. Try to find one that you like and use it everywhere.
Overall, great start. You have a lot of potential to have a solid community.