use Tk;
use strict;
use warnings;

my $mw = new MainWindow(title => "demo");
my $entry = $mw->Scrolled("Text", -scrollbars => 'e', -font => '12')->pack(-side => 'bottom', 
                     -fill => 'both', -expand => 1);
#$entry->bind("<KeyRelease>", [sub {print $_[1];}, Ev('A')]);
$entry->bind("<KeyRelease>", [\&color, Ev('A')]);

$entry->tagConfigure("blue", -foreground => "blue");

MainLoop;

sub color {
   my $content = $entry->get("1.0", "end");
   my $count = 0;
   my @char = split(//, $content);
   my @word = split(/ /, $content);

   foreach my $char (@char) {
      $count++;
   }

   foreach my $word (@word) {
      if ($word =~ /color/) {
         my $len = length($word);
         my $from = "1\.$count";
         my $next = $from + $len;
         $entry->tagAdd("blue", $from, $next);
      }
   }
}