If the green is indeed the chlorophyll from the algae then for sure you
cannot bring the colour back.  Chlorophyll fades if it is not in the
light.  From my knowledge of plants I know that once a leaf yellows
because of lack of light, that leaf cannot be made green again even if
returned to adequate sunlight.
What I don't know is the chemical mechanism -  why does chlorophyll lose
it's green colour?  I suspect it breaks down into something else.
A neat fact - the chlorophyll molecule is eerily like a haemoglobin
molecule except that while haemoglobin has iron at it's centre,
chlorophyll has magnesium.

Nora Bryan
Calgary, Alberta

Lynn Scheu wrote:

> I have experience with cowries that confirms what Bob says...live
> collected cowries, purchased but with animal still inside, that are
> green. Cypraea arabica among others. They have gotten a coating of
> algae...perhaps they were a bit off their feed for a while and didn't
> come out of their shells?  Anyway, then they got well and covered the
> algae with a new and transparent layer of nacre. Bright green when
> purchased. Don Pisor once years ago had a bunch of green arabicas from
> the Philippines. I have seen one of the South African cowries in green
> too, fuscodentata, I think.  They DO fade to gray after a while.
> Sunlight no doubt, and I don't  think there's a way to bring the green
> back.
>
> Lynn Scheu
> Louisville, KY
> [log in to unmask]
> American Conchologist
> Conchologists of America
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