>i found a fair number of the lovely violet form (no
>requests for these, please - like the turquise form of Tonicella and the
>violet form of Neptunea lyrata decemcostata found in these parts, the
>violet pigment quickly fades.  I wonder if these "vanishing" pigments
>are related to each other structurally?

Quite likely. Most shell pigments are quite permanent. My Exilia
(=Surculina) expeditionis was maroon when it came up in the dredge...
and it is now apricotish-mauve, despite having been kept in the dark
the entire time.
--
Regards
Andrew