#!/usr/bin/perl -w

use strict;

my %hash = (
    red    => 2,
    pink   => 1,
    orange => 4,
    black  => 3,
    blue   => 4
);

my %reverse;
while ( my ($k, $v) = each %hash ) {
    push( @{$reverse{$v}}, $k )
}

my @highest = @{ @reverse{
    ( sort { $b <=> $a } keys %reverse )[0]
} };

print join(', ', @highest), $/;