For overall reading, I prefer the old.
I find it easier to use when user information is to the left of the post, and the messages don't have such a large block in between.
Though, I love the new 'Tree' at the top of each block of posts or index showing which forum I'm in. I know the old one showed same info, but not in a tree view.
Example-
+ Ulysses
|-+ General
| |-+ General Discussion
As for colors, well, I don't use them. I viewed the old and the new using another browser I have set to use default browsing colors, and I can't really decide which I like better.
How much work would be involved in using the new menus/headers up to the point of the posts, below the tree line, then using old style for actual message/posts area?