Thought I would chime in on albinism -- from a layman's perpective.
Albinism is actually a bit more complex than most people realize.  In fact,
there are at least three types of albinism, plus the opposite situation of
melanism.

I do not know if the following examples effect shells but in reptiles we
find the following.

1.  Amelanism.  This is an absence of the pigment melanin.  In mammals this
results in a true albino as melanin is the primary color agent in hair,
skin, and even eye color.  In reptiles this results in an absence of black,
brown, and grey and the animal is marked in red, yellow, and orange.  So for
reptiles this is not a true albino.  The eyes are red.

2.  Hypomelanism.  The pigment melanin is reduced, but not eliminated.  This
often means the reptile is still marked in red, yellow and orange but the
eye color is not red.

3.  Anerythrism.  This is the complement of amelanism.  Here the animal is
missing the red, yellow, and orange colors while retaining the black, brown,
and grey.  This is sometimes called axanthic (xanthos is Greek for yellow,
thus "without yellow").

4.  True abinism.  This is a combination of amelanism and anerythrism.  The
animal lacks the red, yellow and orange as well as the black, brown, and
grey colors.  These reptiles are snow white with red eyes.

5.  Melanism.  Of course, the related pigment type is melanism where the
black, brown, and grey predominate and the reptile is typically solid black
in color.

All of these traits are resessive and very complex in the ways they interact
with other genes.  In the reptile world, these traits (plus the patterns of
colors) have resulted in some 50 varieties of corn snakes developed over the
last 20 years in captive breeding.  This means a lot has been learned about
albinism -- at least in reptiles.

In shells, this might explain why some "albino" strombs have a lavender
colors (amelanistic), others orange or red colors (also amelinistic), and
some are totally white (a combination of amelanistic and anerythrism).  I
would assume in each of these cases, the animal would be colored in the same
manner as the shell.  If not, if the animal is normally colored with an
abnormally white shell (or for that matter, a black or dark shell) -- I
would suspect some other mechanism at work.  My first bet would be
environmental.

Tom Eichhorst in New Mexico, USA