Yup, females tend to get .... rather dark blue on their spirals. It's part of their ovary. Of course... I've also seen dark males
Men.... are so often diffcult. Have you had any eggs or is this snail all alone in a tank?
If you see a darker stripe the pulls off the spiral into the white part, thats their intestine. Its dark, but could easily take on a hint of blue if they were feed something green or blue.
There is also a darker line (I can see) in the photo that outlines her 'air pocket' or lung. Just a reflection of where skin meets shell.
She (or he) is awesome. I'm so glad to see her all grown up.
