Sir Ross you wrote;
Few questions about shells get asked more frquently than the old "Since
cowries are covered by mantles most of the time, why do they display
such a range of color and pattern variation: what purpose(s)  does this
serve??" chestnut.  Yet, i have yet to see a convincing   answer.  Any
takers?   For one thing, are cowries really that secretive?  Do they
expose themselves perhaps a little more often than popularly imagined?
 
I once read in a back issue of HSN that cypraea cribraria has a stiking
orange dorsum & white spots and a drab mantle.
The second a predator attacks the cowrie withdraws the drab mantle
revealing the bright pattern, this is supposed to scare the predator.
 
mark
 
"you will never see two hungry cannibals"