What in the world is that??

[megamomx7]

I usually always rinse out the poopy diapers.BUT this last time we were out and I left the poopy diaper in the wetbag in the diaper bag until the next night. After I washed it the stain was black like black mold? Is that what that was? Even If I had not rinsed a poopy diaper and put it in the wet bag I never had that happen...