Why some snais have grey shells?

[Common Blevil]

My konch has grey shell. I know how they look with normal shell. I was thinking that it's just algae, but after i scrubbed some algae off it was still grey. No snails vere harmed, he was just looking funny at me. Conches are not the only snails I've seen with grey shell, a lot of other marine snails in the wild had the same grey color. What does it mean? I know it's completely harmless, but something must cause it, i want to know what!

 

[buttonreefer]

all snails have different pigments found in their cells/mantle that produce the color of their shell.