Long-time readers know of my love of the hearts of whelks.
These are some recent finds, from Nantucket. When you find whelks around here, NYC -- and you do along the long littoral -- they generally are much drabber. The ones I saw in Chincoteague were even darker, a blackish blue, or a bluish black. I believe this is because of the local mineral content, which you can also see in the color of the sand (get up close to it with a loupe or other magnifying glass), the whelks' building block.