Here's a question I think I'd rather put here as if you don't recall the novel I'm trying to find, you might get the question.
We had a new logo proposed in purple and the lady next to me said, "how could they possibly do this in purple, don't they realize it's the mortuary color in Latin America and elsewhere?"

For me purple is a fairly royal color like the color beneath a golden crown. A robe. Culturally it doesn't register as a mortuary color.
But I do recall a novel, I'm thinking it's Mary Stewart or someone like her, who wrote about a village of divers for the shell that made the purple dye in Ancient Greece. Only the purple could be used for royalty.
It was a wonderful story about one of the diver's social ascension.
Does this ring a bell?
One of my favorite things to study as a child for science projects was plant dyes and I won an award on it. So this question came up yesterday and it's really bugging me not to remember the author's name.
I'm almost dead certain the author is a woman.

You must have in mind "The Color Purple" by Alice Walker, which became the Spielberg movie with Whoopi Goldberg and Oprah Winfrey. In the book Shug says to Celie "I think it pisses God off if you pass a field with the color purple and don't notice." The Phoenicians, Greeks and Romans got a deep purple dye from Murex sea snails. And remember the color titles of John D. MacDonald's Travis McGee series? "A PURPLE Place For Dying", "Darker Than Amber", "Dress Her In Indigo", "The Scarlet Ruse", etc. tjoeb};>

My hero! That's where they got the title for the "Color Purple" but the first novel still remains a mystery. It's Mary Stewart or Celia something. It's driving me up a wall now!
You've got the shells bit though! Thank you!
I don't have an English library or I'd find it in a flash.