Beaver pelt gone bad?

I've been freezing my beaver pelts this season to flesh, stretch and dry when I felt fully set up for it. Fleshed, stretched and dried the first one this week...and it's not looking fantastic. Much of the hide has turned a darker color, and there are some black spots. Is this starting to turn?

It felt like I had scraped all the fat away, and had hit a point where what was left was much harder to remove and seemed like hide. This did seem thicker through the lower back.

Drying at around 60 degrees.

Thanks for your help.