Hi, I've noticed two screenshots, on each of them the Barbarian looks different, In one he got warpaint in the other he doesn't?
Is it a new feature that allows you to add warpaint and/or tattoos to your character?
Or has the skin of his model been changed?

Here he got warpaint all over himself

http://us.blizzard.com/diablo3/_images/screenshots/ss126-hires.jpg

And here he ain't got that warpaint.
Personally I like the warpaint much more.

http://us.blizzard.com/diablo3/_images/screenshots/ss131-hires.jpg

The barbarian will see a throwback to the classic blue war paint when equipping a specific gear set.

No, it's just the effect from the chest piece of one 'tier' set.

Class specific items are still planned, but this would not be what it is, no.