Humidity is the most likely culprit, since he didn't shed it one piece last time. You're keeping Marshall in a tank, right? Those can be a bear to keep the humidity in the right place through out the whole enclosure. If he's in blue right now, try adding a humid hide so he'll have the right level of moisture for this up coming shed. For raising it in the whole tank, try adding containers with damp sphagnum moss and/or changing to a substrate that holds moisture better, like cypress. If you have one of those screen top tanks, they will sieve moisture and heat like no other mother, so put some aluminum foil over the screen to trap both.