Looks like some type of bacteria growing under his front limb area? Has he injured himself? How is his substrate maintained? (wet, rough surface?)...How long have you had the tort and where was he acquired from?
I would get a warm water soak going for him, let him soak in the warm water for about half an hour, then take a soft bristle tooth brush (new one) and gently brush that area so you can see the shell...then you can apply some athletes foot cream to the area...you can do this a few times a day and you should see some progress....
The pink lines are new growth, but that spot under the front limb does look like some kind of rot. Is there a smell? Was there an injury?
Since it's hard to tell whether it's fungal or bacterial, I would swab it once with diluted iodine tincture, which will kill anything that's on the surface. Walgreens has it for $3ish over the counter... put equal parts of the tincture and water in a very small container, then dip cotton ball into it, and squeeze it out on this area a few times after soaking and brushing that area w/ an old toothbrush to remove debris. Let the iodine rub dry. Once you've done that, you can treat it with (human) foot fungus cream (active ingredient clotrimazole) and triple antibiotic ointment twice a day. The antibiotic ointment should be put on for about 5 days, the antifungal needs to be put on for a minimum of 2 weeks to be effective (some might say 6 weeks).
Once you've finished the treatment, you can post another pic on here... hopefully improvement will be visible.