We have absolutely no idea what you are working with. There is no galvanized pipe that is 4" o.d., and none of it is "colored" either. What color is it? The rest of your description is also hard to correlate to a normal installation, so a picture may be necessary. In any case, a flange that works for PVC/ABS will also work with cast iron or galvanized, assuming you have standard sized piping.