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

my @bigArray = qw(brown red+green blue+yellow black red+white purple+orange+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__