Earlier this week I was looking at some bivalve shells that had ornate patterns which ranged in color from a light orange-pink to a deep orange-red. Here is an image I found online that seems to be of the same type of shell:
The friend who was with me said, "I wonder where the color comes from." We were trying to look for two shells with similar colors, patterns, and approximately equal sizes, and it was hard, even though we were looking through a large collection of similar shells.
What determines this ornate pigmentation? Is it influenced by environmental factors such as the minerals in the water? Does it have anything to do with the age or health of the organism? Or is it purely genetic? Is this determined by the same basic biological principle that determines the color of human hair, or is there something different at work in shells?