I’ve done a few articles over the years on customizing the team server in OS X Server. This is one of those places where Lion really changes things. Once upon a time you could just swap out the graphics and have a fairly custom-looking wiki or implementation.
In Lion, Apple has really simplified and stripped down the Lion elements in the interface for the server. There is less Apple branding and more functionality than ever. Gone is the time Apple spent building templates, but in the place of all those templates is a much more integrated and functional collaboration server. Added are features dedicated to navigation (e.g. the ribbon was borrowed from MobileMe) document management and writing personal wiki articles. Added is a more seamless integration with podcasts and better ways to find content that is pertinent to you. Also added is a sidebar that allows you to insert blocks, similar to widgets in WordPress, but far less useable (for now).
You can still customize the graphics. They are now stored in /usr/share/collabd/coreclient/public/stylesheets/cc/img. You can also add your own banner or edit the look and feel in the css files stored in the /usr/share/collabd/coreclient/public/stylesheets/cc. For example, editing the core.css file to change the color (not background-color) setting in the body section will change the color of the text (use my color chart to pick a new color if you’d like). Also in the core.css file is the background color for the unused space, located in the background-color setting of the main section. The blue title bar for wikis can also be customized to include a background image or just change the color. For example, use the banner.css file to add the background-color field into the banner section with #FFFFFF to set that to white.
As usual, be careful when customizing Apple’s services. Personally, I find that whenever I customize their settings, I end up making them look worse. Apple is known for design. If you’re looking at my web site, you’ve likely noticed that I am not. If you decide to walk down this path though, I have a good tip. Use a browser plugin for Firefox to help you. You can make changes on the fly, see what works and what doesn’t and gradually change settings until you find a look and feel you can live with. I like Edit CSS, but as with many of these kinds of things, it’s just preference – search for CSS in the Firefox add-ons for one that you find that you like better.