my @array = qw(red green brown);
use vars qw(%hash);
foreach (reverse @array) {
    *hash = { $_ => (%hash) ? \%hash : 1 }
}

##</code><code>##

my @array = qw(red green brown);
my %hash;
foreach (reverse @array) {
    %hash = ( $_ => (%hash) ? { %hash } : 1 )
}