He had some retained shed for a week or so (his whole body and tail shed except for the last half of the tail), and some of it came off today - and it is very dark underneath it.
Is this normal for the situation ? Should I be worried ?
There is still some shed on the very tip of his tail. Could this single layer really be causing a big problem ? I have been giving him baths and gently trying to help, but I do not want to pick at it. Should I be more helpful ?
It is noticeably darker, but it doesn't look like tail rot if that's what you are worried about. It won't hurt to start a diluted betadine bath (1 part betadine, 10 parts water) just in case it is the very start of an infection though. Obviously continue to keep an eye on it. If the tip starts to shrivel or the darkness spreads any farther up the tail, I'd get it checked out by a vet. Hopefully it's just a natural change in coloration but it never hurts to be extra precautious.