That's what I've observed. The first time I saw those crevices i panicked a bit thinking my tort was splitting lol, but it fills with keratin that is white, as the new keratin hardens it darkens. But if your tort is kept bone dry it won't fill the crevice causing pyramiding. This is where humidity plays it's part. Those that live in Florida naturally get high humidity and rainfall with warm weather, we don't. Well we get the rain. Lol. So you need to imitate that in your enclosure. I soaked my hatchling every day for 15mins up to 12wks old. Now 3 times a week. That's why I asked how big your tort is. Do you know it's age, where did it come from? If you don't know it's history I'd soak it ever day for a week or so to make sure it's well hydrated.@Anyfoot
So, just to check I've understood- do I want to see those crevices infilling and essentially turning white?
The little chap has currently decided it's lovely and cosy snuggled behind a large bromeliad down the warmest end of his enclosure.