Tk dosn't have themes yet, like Gtk2, but you can setup default options, and you can probably design some nice color combinations.... I prefer limegreen, hot pink, and black ;-)

#!/usr/bin/perl -w
use strict;
use Tk;

my $mw=tkinit;
$mw->optionAdd("*background"=>'lightblue','userDefault');

$mw->Listbox->pack->insert(0,qw/a listbox/);
$mw->Text->pack->insert('1.0','text widget');
$mw->Entry->pack->insert(0,'entry widget');

MainLoop;
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