use strict;
use warnings;
use HTML::Template;
use CGI qw(:standard);

my @color = qw(red green blue black purple orange);
my %valid = map {$_ => 1} @color;
my $tmpl  = HTML::Template->new(filehandle => *DATA);

my $color  = param('color');
my $select = popup_menu(
   -name    => 'color',
   -values  => [@color],
   -default => $color,
);

$tmpl->param(error => 1) unless $valid{$color};
$tmpl->param(
   colors => $select,
   color  => $color,
);

print header, $tmpl->output;

__DATA__
<form>
<p>
Pick a color:
<tmpl_var colors>
</p>
<input type="submit">
</form>

<tmpl_if color>
   <p><hr/></p>
   <tmpl_unless error>
      You picked 
      <span style="color: <tmpl_var color>;"><tmpl_var color></span>
   <tmpl_else>
      Invalid choice, "<tmpl_var color>"
   </tmpl_unless>
</tmpl_if>
[download]

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)