Abnormal black patch on rainbow millipede - course of action?

[Delight]

I am fostering a rainbow millipede in an effort to see if it is possible to nurse it back to health. It has a black patch on its side, about midway down the body that almost looks as if the tergites are pulling away from the body. I'm uncertain what to do about it. The tissue definitely appears to be dead, but he's still active and regularly mobile.

I've isolated him from the colony (taken him back to my apartment) and put him in a clean critter carrier living on paper towels that are regularly changed. He's eating bananas and fish food and occasionally squash and things like that. I'm avoiding anything that is citrus or acidic. He is being kept in a warm and very humid container in an effort to speed metabolic processes. His location has day and night temperature cycles as well.

Is it possible to identify what this is?
Will it be solved by a shed? When will he shed? He's been like this for 9 weeks or so with no shed nor change. I'll get a good measurement of his body length.
Is there anything that can be done about it?

I will try and get a photograph of the spot, get temp measurements, and physical measurements of the critter.


(I have named him Space Cadet and have become rather attached.)

 

[Elytra and Antenna]

Black damage spots are pretty common on millipedes though more often on wild ones than captive bred. Usually it's not a problem and can go away in a molt or two.
What's your avatar image? It looks likes a yellow mantis face with a purple chicken starfish body?

 

[Delight]

The avatar is actually a gorgeous picture of an adult mermelontidae. It was the first good photo of an adult one that I've had the pleasure of seeing.
http://caterpillarblog.com/page/3/ is where you can find the photographer. She's also weirdbuglady on etsy if you wanted to see her plush tardigrades and centipede scarfs that she makes.



EDIT: I almost forgot.. It's a HUGE relief to hear that it is something that happens regularly and doesn't mean certain death. This did appear and wasn't on the diplopod initially. It developed somehow during captive care.