if it's turning blue that part of the tail is probably going necrotic and will turn black.
The medicam isn't needed for the neuter at this point unless there were complications with that, buttttt it is probably relieving any pain from the tail and helping him from going after his tail.
The only thing that can be done at this point is preparing an e collar in case you need one if you haven't already. The vet may or may not do anything about it just yet so if you take him in don't be upset if they don't do anything but examine him.
They may or may not keep him on the pain meds, and an antibiotic.
Some vets will hold off on amputating depending on where the injury is on the tail until the tail fully goes necrotic. Sometimes once fully necrotic that part of the tail simply falls off or they clip it off. In your case, that is likely what they will do because it is more likely to fall off or simple clip off without surgery.
Other times it continues going up the tail, so the vet waits so they aren't amputating twice.
Gliders with amputated tails or tails that fall off from being necrotic usually make a full recovery and go on to live very normal thriving lives, just with a shorter tail. They don't have ghost pains from amputations.
He will likely need an e collar if they do amputate to prevent him from bothering the site, which isn't considered self mutilating. It is considered to be normal behavior for injured and recovering gliders. Once it's healed he won't go after it again.
At most it's irritating to gliders that were tail carriers because it's frustrating they can't wrap their tail around like they used to.
E collars are pretty simple to make, the supplies, directions and template can be found here
http://gliderhealth.com/slfmutl/ecollar.html
If you don't have those supplies you can improvise, we actually prefer mole foam tape for the neck part. The cone should be something a little stiff, in a pinch we have used bottled water bottles and they work greatt.
Getting the collar on him probably isn't going to be easy.
There are things you will need to do for him if he does need an ecollar, he will need access to food and water with the e collar on we use bird water silos for both food and water. He will need an OE pouch instead of normal pouch and it should be lower to the floor for easy access. You will need to keep the inside of the cone clean, qtips work well and you may need to clean his fur from the neck back for him while in the collar.