The case comes in Charcoal Gray or White and is compatible with iPhone 6s or iPhone 6.
The battery case includes a passthrough so you can still plug in other Lightning accessories whilst the case is in use.
The additional thickness of the iPhone 6s Smart Battery Case appears to add about 7 mm to the 7.1 mm iPhone 6s.
The Apple Smart Battery Case is only available for the 4.7 inch iPhone 6. Apple has not released its own case for the iPhone 6 Plus, presumably because the Plus naturally gets higher battery life due to the larger internal battery.