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You may not like the color of the group divider bar -- it's a very flat gray, and Thankfully, it's pretty easy to change, as the resources are simply images in the iChat application bundle. More specifically, quit iChat (if you're going to make any changes), control-click on iChat and choose Show Package Contents, then navigate to Contents -> Resources. Modify these four files:
As always when tweaking an application, start by making copies of the files you're going to modify, in case you want to reverse the changes later. I chose to make the dividers a "Tiger-like" blue gradient -- you'll want to use a darker color in general, as the text for each group is white. Edit the files in your favorite graphics package, then re launch iChat to see the results of your work.
Taken From: MacUpdate
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