But Tk is only really ugly on Unixen because it defaults to a Motif theme (modern Tk is/should be replaced by TTk which is themeable).
Given two Tk apps which I still use occasionally, namely Gitk and ptkdb, how do I change their look and feel so that it matches the rest of the desktop environment (KDE 4)?
Check out the TkDocs website, everything I know about modern Tk I learnt from there! Well and experience too of course ;-)
It will not be simple to retrofit it onto a substantial legacy application, but you could probably get surprisingly far by just prefixing the widgets with ttk::.
See: http://wiki.tcl.tk/gtklook.tcl for a quick way to make default Tk look less painfully ugly. I often use it in my own programs to hide the fact that it's actually written in tcl/tk.
The code given is tcl but you can easily use the options in an Xresources or Xdefaults file which I think should work in other languages as well. Or, it that doesn't work I believe there is an equivalent option method in Perl/Tk*.
Yes, the changes are not much. Basically just reducing pixel widths of things like borders and scrollbars. But it does look much nicer.
*note: I only mention Perl/Tk because you mentioned it in another post. As for modifying gitk, it is written in tcl so you can easily copy-paste the code somewhere.