Cat- blue tail (skin)

Question
My cat's tail got bit 3 weeks ago; I took him to the vet and got 2 weeks worth of antiboiotics.  I gave him all his medicine.  A couple days later, the skin on his tail turned blue, so I took him back to the vet.  My vet has no clue what is wrong, but he said it's abnormal.  The vet did bloodwork, and my cat is healthy in every other way (no infection); my cat and I were sent home with no answers.  Now the blue skin is from where the bite was (near the base of his tail) all the way to the tip.  Do you have any idea what this is?  I don't want him to lose his tail.  

Answer
Hello!

It sounds like it may be necrosis, in other words the skin where the bite wound is dead now, because it could not be fed by enough blood or it may be due to a fracture on the tail bones which would also cause to poor innervation. If it is simply on the skin, without any broken bones, the skin will gradually start to come off for the new fresh skin regeneration. But of course I am only assuming these, since I haven't seen it. If there is a broken bone and this is the reason, the part which stays on the bottom of the broken bone may die totally, and it may be amputated with surgery. Can he move his tail? Or does it drop on the floor like it is lifeless?

Kind Regards