What color wires was the original fixture connected to?
Wrong Greg. The neutral cannot be switched and has not been done that way for many many years.Switch legs save on wiring. Nothing unusual about it. Very common to allow you to also feed off of BX at that time and even now with Romex to allow a third wire to allow another lighting fixture or outlet to be powered off of that incoming power into the ceiling box.
It is not against the code to have that fixture wired up like that, because you are using the Neutral as the leg for the switch. The only gig on the code, is that they did not id the White for the Neutral as either Black or Red, to designate it as for the Switch leg to the switch and at the switch.