I'm new here, so I feel a bit guilty criticising things. But I've these suggestions, so please, bear with me.
For starters: the new themes are definitely a huge step forward. The warm one is my favourite. But, do we really need three (now: four) of them? I'd rather see one that gets all the attention. I had dealed with sites with a selection of custom skins. Believe me: it's not worth it. Updating and maintaining one is hard enough.
So, I would ditch warm and modern, leave the classic and put all the focus on it. Let the community work on the alternatives. And don't wait too much with the release. Ship it once it reaches a stable stage, let the people iron out the details.
Speaking of the details (sorry again for nitpicking):
1) The header is too tall. The title is not that important to take over 15% of the screen estate. Footer as well could have significantly smaller vertical padding. Bascially, the content should dominate over everything else. In the era of small handheld devices it's very important to not waste any vertical space.
2) The colors are nice, however they're a bit imbalanced. It's a question of small details. Like: why the title is pink? If it's not a link it should be black.
Take for example this forum. It has similar palette and yet it looks way clearer. I'd take clues from it.
3) Items in the pages' tree could use an icon to show if they're closed or open. A simple triangle would do the job.
I'd like to repeat that overall the new themes are great. I love the fact they not change things in a revolutionary manner. If anything, I'd make even less changes and introduce the new things in a few small steps. But, again, Ryan, you did a superb job.