Quoted from LTG:
If it's a reaction in the paint, it all changes. Not just an area.
I had an O Scale model railroad engine painted in Freedom Train colors. Over time the bright white faded to cream color, engine and tender. both sides. And it was sitting on a shelf all the time. So both sides had different exposures.
LTG : )
Well, if there is some chemical process that changes the white to cream on some playfields, then I suppose it is possible that my playfield was white in 1982 and changed to cream by the time I bought it in 1984. All I know is that I have an original playfield that has been cream for a long time.
When I got it, it was pretty badly worn and had a thick piece of mylar covering just the area between the slingshots. I removed that mylar, did quite a bit of touch-up to various worn areas, and then installed the full thin mylar sheet (which I had to order from Bally through Betson). The mylar'd area has held up quite well over time, but the areas not covered have gotten worse.
Eventually I will do either a swap or a hardtop (probably a swap), but that's a project for the future.