#!/usr/bin/perl -w
use strict;

my $key;
my %hash = (
             ball1 => 'red',
             ball2 => 'blue',
             ball3 => 'red',
           );
# thanks to http://www.perlmonks.org/index.pl?node_id=340896 for this block of code

my %reverse_hash;
foreach $key ( keys %hash ) {
    $reverse_hash{$key} = $reverse_hash{$key}
                        ? "$reverse_hash{$key},$hash{$key}"
                        : $hash{$key};
}
print "$reverse_hash{red}\n";