Easy - the forum colors. Think the colors goes better for heavy reading (or as heavy as the posts allow that is..).
The mainsite colors are good for layout and not so much reading. But for the forum to follow I would hope not. It's one of the things I dislike about tatu. us for instance the dark colors that isn't too nice for one to read text at. Too little contrast I think the problem is, or too much?
Could be I'm too conservative and want to keep the things I'm used to. I never really got used to the mainsite colors since I don't really visit it that often. Think last time was when the new layout was intoduced