Hmm that does look odd. What's it like? Have you tried gentle scrubbing or anything? Have you seen it dry? I'm no expert on shell conditions, but those seem like useful questions.
Adrienne!
2.0 RES: Turtley and Samson
1.0 Lutino Cockatiel: Lilly
assorted fish, hermit crabs, bugs etc.
That dark area in the seam between the two scutes in the middle and also a big toward the right? I'd take a moistened q-tip and see if it can't be cleaned. The shell looks nice---is there a darkened area on the other side of the scute toward the neck as well?
"You become responsible, forever, for what you have tamed." -Antoine de Saint Exupery-