Not cased in a different colour or clear. You can see the top of the second casing, Paul - it's that bulgy bit at the base of the neck. An initial thin bubble would be blown, and the neck shaped at the top of it, then the body is given an extra partial casing, up to the base.
(I think when it's referring to bottle making, the expression "on the post" is meant to be accurate. I still just think it's completely confusing - especially after somebody explained it wrongly and the story got around that the bottom and the neck are made seperately and then the neck is "dropped" into the bottom - utter nonsense!)