Soap scum on fiberglass

From reader BlondeMom:

I have the same inserts and you cannot scrub the walls because it scratches them and they lose that shiny finish. I got a real inexpensive cleaner at KMart (called "The Works" and if I remember correctly it has a white label with green lettering); it was cheap (approx $2) and cleaned better than any of the big name brands. My girlfriend and former neighbor just suggested a product called "Greased Lightning." It comes in a white spray bottle and cleans everything, leaves it shiny and smelling good! Hope these suggestions help!

From reader sully7:

I have old fiberglass showers in my house and have tried alot of things to get them clean and keep tham that way. I also have 4 small children and need to have as little chemicals as possible. For my showers I use warm vinegar in a bowl and scrub with one of the non-abrasive pads. I try to soak the walls as much as possible. It is amazing what comes off! The walls actually shine!! The smell is strong but it goes away pretty soon and an added benefit is that the vinegar kills any mildew!

We have a one piece shower unit.My husband ask me what causes that nasty orangy-pink film that sometimes gets on the bath tub where the shower walls meets the tub. I tried to explain that it is caused from soap residue. Do you have a better expaination? Thanks