For what its worth, in my opinion in the case of 2 wire romex it is much more obvious to use the white wire as the line that is grouped with the hots and run to the switch and the black wire as the line from the switch to the fixture. As was pointed out in the last post the wiring at the fixture has the normal "black and white" wires run to it. More importantly, the white wire grouped with the hots gives the fact away that the white wire is being used as part of a switch leg and the black wire joined with it in the romex should be attached to the fixture -- makes doing any trouble shoot work a snap.
