I have 2 blues that I bought at a local pet store that changed their shell coloring and thickness after I started feeding them snail jello.
I've love the photos of blues that some people post on here- then I see them in the store and they are a mucky grey colour. I've wondered if they could be conditioned to have nice shells from the petstore or if they stay that colour.
... although, I don't know if I would ever get one from a store with all the colours being readily available on here.