I'm glad he ate for you.
A snake's tail doesn't go into blue before the rest of the body. The whole body goes dull, then "blue", then clears-- not just a part. It's hard to tell from the photo, but it almost looks like he may still have unshed skin from his last shed on his tail. Since he just ate, you'll need to wait a few days before messing with him, but you're going to need to remove that skin (if I'm seeing things correctly). You can leave him in a small tub of moist moss or paper towels overnight, and if it doesn't come off itself, you may have to work at it with a damp paper towel.