#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11163827
use warnings;
use Tk;

my ($red, $green, $blue) = (0, 50, 100);
my %colorhash = (Red => \$red, Green => \$green, Blue => \$blue);
my $mw = MainWindow->new;
$mw->geometry( '300x100+500+400' );

my $row = 1;
for ( qw( Red Green Blue ) )
  {
  $mw->Label(-text => $_,
    )->grid(-row => $row, -column => 1, -sticky => 'w');
  $mw->Label(-textvariable => $colorhash{$_},
    )->grid(-row => $row++, -column => 2, -sticky => 'e');
  }

my $color = 0;
$mw->repeat( 1000, \&change );
$mw->repeat( 1777, sub {-M $0 < 0 and exec $0}); # restart when code changes
MainLoop;

sub change
  {
  ( sub { $red = int rand 50 },
    sub { $green = 50 + int rand 50 },
    sub { $blue = 100 + int rand 50 }
  )[ $color = ( $color + 1 ) % 3 ]();
  }