Hi Elizabeth -
 
Kind of depends on what you mean by "bleached".  Ordinary bleach
(such as Chlorox) does not remove colors from shells; in fact bleach
is commonly used in cleaning shells.  Therefore a "bleached"
specimen, in this sense, is not white, and would not be confused with
an albino.
A second meaning of "bleached" is "sun-bleached", a shell which has
been on the beach baking in the sun for some time, and has had its
pigments destroyed by ultraviolet radiation and heat.  Such a shell
is usually not too difficult to tell from a live-collected albino
because (1) seldom are the pigments completely destroyed - there is
usually some evidence of the original color and pattern visible, at
least when the shell is wet, and (2) any shell which has been on the
beach long enough to become sun-bleached is likely to be somewhat
weathered by rain, wind-driven sand, etc., and is likely to show some
degree of pitting, reduced gloss, etc., which clearly mark it as a
"beach shell".
A third form of "bleaching" is the deliberate destruction of pigment
by baking a shell at high temperature, to produce an apparent albino.
 When I read about this some years ago, I tried it a few times myself,
just to see if it worked.  I placed some expendable shells on a rack
and baked them in the oven at about 300 degrees F (149 degrees C) for
an hour.  Then, to avoid cracking from sudden temperature change, I
turned off the oven and let it gradually cool, without opening it.
Shells having a dark pattern, like Babylonia areolata or Terebra
subulata showed substantial lightening of the colors.  However,
shells having fairly light patterns, like Conus textile or Oliva
reticularis came out pure white or very nearly so.  The olives in
particular, I would have to say, would be difficult to tell from
natural albinos.  Something to keep in mind if someone offers you
albino specimens.  True albinos do occur in many species though, and
in some species, such as some of the cockles (Cardiidae), they are
fairly common.  There are only two ways to know the relative rarity
of albinism in a particular species - hit the books, or ask on
Conch-L.
 
Paul M.