Merlyn has already posted a better solution, but in the interest of TMTOWTDI here's one using Data::Dumper:

#!c:/perl/bin/perl -w
use strict;
use Data::Dumper;

my $our_hash = {
    'Cows' => {
        'Brown' => undef,
        'Green' => undef,
        'Strawberry' => {
            'Spotted' => undef,
            'Solid' => undef
        },
        'Orange' => undef
    },
    'Dogs' => {
        'Purple' => {
            'Spotted' => undef,
            'Solid' => undef
        }
    }
};

$Data::Dumper::Quotekeys = 0;
for (Dumper $our_hash){
    s/\$VAR1 = //;
    s/{/<UL>/g;
    s/}/<\/UL>/g;
    s/(undef)?[,;]?\n/\n/g;
    s/\n *([^\n]*)=>/\n<LI>$1<\/LI>/g;
    print;
}
[download]

Not really pretty or robust, but it works with a simple hash like your sample ... you'd need to flesh it out a little if you wanted it to be able to handle quotes, etc. Like I said, Merlyn's solution is better, but I couldn't resist giving this a try...

Update: Added closing </LI> tag per flocto's encouragement.

-- grummerX