It looks like the belly is from being on newspaper that got wet.
If a ball gets out of its water bowl or spills its water and then sits on newspaper the soy in the paper terns the belly pink/red.
We see it happen when babies are first soaked and then put in a tub on paper while they are being sorted, you will always get a couple that get pink bellies. We have had about 6500 baby balls in the last 3-4 years and have had about 20 with the pink/red bellies and they always shed out.
It can also happen when a larger snake urinates in a bag with newspaper in the bag.

Its always a surprise to see, but will always shed out too.

On the non feeder we always have really good luck offering them smaller fuzzy mice in a dark shoe box. If that does not work try it in a shoe box inside a blanket box, as it will creat a environment with a high ambient temp without the same affect as heat tape. The difference in the types of heat really seem to kick them into gear, and usually turn most non feeders around.

Good luck.