Tk itself, does not support transparency, but Tk::Zinc does. Another alternative is to move up to Gtk2 or Gtk3, which does handle transparency. For example see: Goo Canvas and transparent images

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

my $width = 100;
my $height = 100;

my $mw = MainWindow->new(-background => 'cyan'); 
$mw->geometry($width.'x'.$height.'+300+300');
$mw->overrideredirect(1);
my $zinc = $mw->Zinc(-width => $width, 
                     -height => $height,
                     -reshape => 1,     #clips zinc
                     -fullreshape => 1,  #clips $mw and xterm
             -backcolor => 'cyan',
                       )->pack; 
                 
#make a flower 
my $petal = $zinc->add('curve',1,[[$width/2,$height], [0,0, 'c'], 
                                 [$width,0, 'c'], [$width/2,$height]],
                   -tags => ['bezier1'],
                   -filled => 1,
                   -fillcolor => 'cyan',
                   -closed => 1,
                   -linewidth => 0,
           -priority => 1,
           -visible => 0,
           );

# using the triangulaire curve to reshape both TkZinc and Mainwindow w
+idgets 
$zinc->itemconfigure(1, -clip => $petal); 

my $petal1 = $zinc->add('curve',1,[[$width/2,$height], [-2*$width,-100
+, 'c'], 
                                  [3*$width,-100, 'c'], [$width/2,$hei
+ght]],
                   -tags => ['bezier1'],
                   -filled => 1,
                   -fillcolor => 'cyan',
                   -closed => 1,
                   -linewidth => 0,
           -priority => 1,
           -visible => 1,
           );

&Tk::MainLoop;
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