You should be able to determine if the dark portion is body tissue or not...
If it has white at the end (the first end to come out) and the black part looks sorta like an olive pit - then it is most likely feces. The feces may be hard due to lack of water in his system - a slight case of constipation. Of course, there could be other reasons, as well.
Try this: holding the cham - soak his back side in some warm water - not hot - but comfortable on your skin. You can do this in the bathroom sink, if need be. After a few minutes, see if you can dislodge the matter with a tissue or Q-tip.
If this is unsuccessful, soak him for a bit longer. If you are still unable to dislodge it - consult your vet.
If it were a sperm plug with his hemipenes showing, the tissue would be bright dk pink or red. If it were sperm - it would look like dried hot glue - and it would be stringy - stiff, yet rubbery. Sometimes a male cannot force the sperm completely out when they clean their hemipenes and it dries in the cloaca. These plugs can be removed by gentle, slow, steady pulling - and/or soaking.
The only black hemipenes we have seen were on a melleri - all the panthers are dk bright reddish - some a bit of a purple cast. Males regularly clean their hemipenes after sexual maturity. We find sperm plugs on branches often.
It usually takes several hours for a prolapse to turn black with necrosis - but one should use a good lubricant to keep it moist (not vaseline).
Keep us posted.
-----
