Well, thinking just skin, cause on the Tauren you just change skin... so I assumed the same for Worgen.
I worry about changing anything else, cause you don't see at the same time what your human will look like.
No, I haven't tried Hair colour, assuming it was to change the human hair.
Yeah, it is linked to the human form's hair color, there are pic floating around that shows the correspondance between hair and feral form colors.
It is actually nice because it allows you to customize the color of your feral and worgen forms independently.
The downside is that the barber shop isn't really well polished for worgen at the moment and provides no way to see your human form's hair color but allows you to change it.
I suggest going to worgen character creation and write down the cycling order of hair colors so you know how many times to click prev or next in the barber shop to get the hair color you want.