Healing wound. What is the white around the edge?

Here's an example of a wound that is been healing. I just saw this patient one week ago and was larger and I can tell that it's getting smaller. But there's a portion of whiteness around the wound that is the callus starting to go back. Today I had to remove that callus and continue to have the patient stay off the foot as much as possible.

Hopefully this will be healed in a few more weeks and then he can get back into his diabetic shoes.