Hello,
I hope this doesn't classify as an "advertisement", but your question is most
timely.  In fact, uncannily so!  A couple of days ago I received a black
Murex ramosus, and just THIS MORNING I prepared images of it, for the next
MTP online auction.  Of course, "black", as it pertains to melanistic shells,
it not technically accurate.  Molluscs do not produce true black shell
pigment.  When they look black, it is due to extremely heavy concentrations
or brown, or even red pigments.
Regards,
Paul M.