Concerned

My cat had surgery about three weeks ago and I have noticed that where his IV was inserted, it is now completely black on his skin. Is this normal or should I be worried?

The best thing to do is just phone the vet. @olivertwist  . People get bruises all the time from needles, and they change colour, too.  So it may not be anything more than the skin underneath healing from the I.V. site, but I would call just to be sure.

If it is an "infection" at the site of the needle mark, this would also cause discoloration, and would need further antibiotics, so best to contact your vet.