Hybrid will never become pure BD. However, some hybrid may look identical if not better then normal BDs and are highly sort after.
Nowadays its hard to tell if a BD is really pure or not as there are too many high quality hybrids out there. Thus just buy what you like and be happy with it.
If base is black it normally will not change lighter. If lighter base normally will turn dark base as it grows.
Just my 2 cents.
Regards