To repeat a node above, doing this with regex seems a little odd. Anyway, I thought I would take 5 and have a go. I did mine with look behinds (cos I rarely get to use them and its different to your solution). Not sure if my attempt is bone headed :). Still . . . here it is:

use strict;
use warnings;

my @nums;
for(my $i = -100; $i < 400; $i++)
{
    push @nums, $i;
}

foreach my $n (@nums)
{
    if($n =~ /^[012]?(((?<=2)[0-5])|(?<!2)[0-9])?(((?<=25)[0-5])|(?<!2
+5)[0-9])$/)
    {
        print $n, ": pass\n";
    }
    else
    {
        print $n, ": fail\n";
    }
}
[download]

HTH