There was a discussion of this recently in comp.lang.perl.tk. Go to groups.google.com and search for "Tk vs Anythign Else?". There are some code samples in the thread. The problem is portability. It's easier to make skins if confined to 1 window manager, like KDE, but Tk is designed to run under any window manager.

For what it's worth, some of the guru's there claim "they are working on it".

It would be easier and more portable to do what Podmaster suggests. Just make a set of graphic templates, to place on canvases, and you can make any theme you want.

You could also probably work out a scheme of setting ENV variables, which would define your color preferences, and write your code to read the ENV. But it wouldn't work for other Tk apps which you run.