I swim across these giant clams with regularity. I always take a shot. They aren’t swimming away. But they close up. The key is to get that opening to the left; it’s a mouth or excretory organ. The color varies, blue, brown, and some occasional red tints. I don’t usually see green. The algae are a factor in determining color. Reproduction has been on my mind. The clams are in a fixed location widely separated. This must be quite a challenge. As far as eating, which my father would have certainly considered it. Do the colors affect the taste?