use Tk;

my $mw = new Tk::MainWindow;
my $c = $mw->Canvas(-width => 300, -height => 100)->pack;
my $text = $c->createText(20, 20, -text => 'A text item');

my $but  = $c->Button(-text => 'Push me!',
		      -command => sub {
			colour_text('red');
			$mw->after(500, [\&colour_text => 'black']);
		      },
		     );
my $but_i = $c->createWindow(70, 50, -window => $but);

MainLoop;

sub colour_text {
  my $colour = shift;
  $c->itemconfigure($text, -fill => $colour);
}