The optionAdd mechanism isn't fully foolproof. You may have to manually add the options to each widget. Each widget will act a bit differently. You might also want to ask on comp.lang.perl.tk, where someone else may know a useful trick or two. As you can see below, the highlightthickness only works on a per widget basis.

It may be a bit late now, but Gtk2 has better uniformity of control over all widget parameters, in Tk, each widget has a distinct personality.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $mw = tkinit;

$mw->optionAdd('*foreground' => 'yellow');
$mw->optionAdd('*background' => 'black');

$mw->optionAdd('*borderwidth' => 0);
$mw->optionAdd('*insertborderwidth' => 0);
$mw->optionAdd('*selectborderwidth' => 0);
$mw->optionAdd('*highlightthickness' => 0);
$mw->optionAdd('*hightlightcolor' => 'black');
$mw->optionAdd('*selectbackground' => 'black');

my $f = $mw->Frame(-borderwidth => 0,
                   -highlightthickness => 0,
                    )->pack(-expand => 1, 
                         -fill => 'both',
                         );

$f->Label(-text => 'First label')->pack;

$f->Text(
  -highlightthickness => 0
  )->pack;

my $canvas = $f->Scrolled("Canvas",
  -highlightthickness => 0
)->pack();

MainLoop;
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