Almost no change:

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

my @bigArray = qw(brown red+green blue+yellow black red+white purple+o
+range+gray);
my %hash;

for (@bigArray) {
    my @keys = split /\+/;
    my $ptr = \%hash;
    $ptr = $ptr->{$_} ||= {} for @keys[0..$#keys-1]; # work done here
    $ptr->{$keys[-1]} = 1;
}

print Dumper(\%hash);
__END__
[download]

Output:

$VAR1 = {
          'blue' => {
                      'yellow' => 1
                    },
          'purple' => {
                        'orange' => {
                                      'gray' => 1
                                    }
                      },
          'brown' => 1,
          'black' => 1,
          'red' => {
                     'green' => 1,
                     'white' => 1
                   }
        };
[download]

Key change vs the code I posted in your previous node is use of ||= vs = so that a key is only assigned an anonymous hashref when it doesn't already have a value. (Which isn't quite right; it's only assigned a hashref when it doesn't have a true value, but that will work so long as any value a key can ever have is true. Here they can only be either hashrefs or the value 1, both of which are indeed true.)

Makeshifts last the longest.