$ perl -le'
my $str = "A: Gold, Black, Purple, Blue, Red     B: Black, Neon Pink, Neon Yellow, Neon Green, Neon Purple, Red, White, Neon Orange, Navy";

my %hash = map s/:// ? $_ : [ split /\s*,\s*/ ], grep length, split /\s*(\w+:)\s*/, $str;

use Data::Dumper;
print Dumper \%hash;
'
$VAR1 = {
          'A' => [
                   'Gold',
                   'Black',
                   'Purple',
                   'Blue',
                   'Red'
                 ],
          'B' => [
                   'Black',
                   'Neon Pink',
                   'Neon Yellow',
                   'Neon Green',
                   'Neon Purple',
                   'Red',
                   'White',
                   'Neon Orange',
                   'Navy'
                 ]
        };