My wall  has one black wire and one white wire, also a green ground wire coming into to box.   I had to wire the HS200 with one black wire connect to black incoming and the other black HS200 wire to the white incoming wire.  I then wired the HS200 white common wiire and the green HS200 to the green ground wire from the box.   

Everything seems to work fine and looked up to wi-fi okay also.    My guestion is it is okay for the white common wire on the HS200 switch and the green ground wire be connected to the green ground from the wall box.