I'm not sure if bivalve species with heavy periostracum produce albinos or
not - but one point that should be made is that the periostracum of an albino
shell will not be white.  Neither will the operculum.  The shell is made of a
white material - calcium carbonate - which becomes colored only by the
addition of pigments.  Therefore the lack of these pigments leaves a white
shell, an albino.  However, the base material of periostracum and operculum
is a yellowish brown material called conchiolin.  It is not brown by virtue
of pigments mixed in - it is just a brown material, the same way sulphur is a
bright yellow material or coal is a black material.  In most species there is
not additional pigmentation in the operculum or periostracum.  Therefore an
inability to produce pigmentation would not affect the color of the operculum
or periostracum.  An exception would be gastropods which have an operculum
made of the same material as the shell, like Turbo, Natica, or Nerita.  In
these species, an albinistic shell would probably have an albinistic
operculum.  Has anyone directly observed this?
Paul M.