hi...each widget in Tk seems to respond to a different set of options.... its a haphazrd collection of options.... so here is another little secret

read perldoc Tk::options and see the other options available ( that the Tree author didn't put in his docs).... there is an option for "highlightthickness".... you might see if that works, put a value for 0 or 1 in there and see if it helps.

...as to the other trick, about matching colors...in Tk::options there are some options for background and highlightbackground colors..... they may not respond to the Tree though....that is the trouble with Tk.....it's not a coherent widget set and inherited object system...... next project, think Gtk2