If you can cope with an array, something as simple as /([^:]+)+/g should do the trick.

my $c='aaa:bbb';
my @arr = $c =~ /[^:]+/g;
use Data::Dumper; print Dumper \@arr;
__END__
$VAR1 = [
          'aaa',
          'bbb'
        ];

---

my $c='aaa:bbb:foo:bar'; 
my @arr = $c =~ /[^:]+/g;
use Data::Dumper; print Dumper \@arr;
__END__
$VAR1 = [
          'aaa',
          'bbb',
          'foo',
          'bar'
        ];
[download]

Update: Simplified the regex, as per Sidhekin suggestion.