http://www.worldofballpythons.com/morphs/black-head/

If you can't tell the difference between this and a normal I'm afraid you'll need more experience with many of the morphs that are out there. There are a lot of morphs that can be described as "looking normal" which, in my opinion, just means that one isn't looking hard enough.

A black head has, as you can see in the pictures, a black head as opposed to the brownish sometimes blushed head of a normal. Another key indicator is the pattern and characteristic black back. The classic alien heads become single eye heads or erratic all together, not to mention the increased melanistic look to the snake all together. It also tends to have intense flames coming up the sides as well.