use strict;
use warnings;

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

my %arrays;

my( @substrings ) = $str =~ m/(\w:\s*.+?)(?=\w:|$)/g;

foreach my $substring ( @substrings ) {
    my( $key, $colors ) = split /:\s*/, $substring;
    my( @colors )       = split /,\s*/, $colors;
    $arrays{ $key } = [ @colors ];
}

foreach my $key ( sort keys %arrays ) {
    print "Array $key: @{$arrays{$key}}\n";
}