#!/usr/local/bin/perl -w
use Tk;
my $mw = MainWindow->new;
my $t = $mw->Text(-background => 'yellow', -width => 30, -height => 10);
$t->pack(-expand => 1, -fill => 'both');
$t->insert('1.0','This is Text','Atag');
$t->tagConfigure('Atag',-background => 'green');
$mw->Button(-text => "Change Colour",
            -command => sub { $t->tagConfigure('Atag',-background => undef) }
           )->pack;
MainLoop;