My guess is that if the 20-pocket page was NON PVC ... this common problem may not have happened. It is the PVC in the plastic PAGE that sucked out the color of the chip ... not the mylar window of the 2x2 cardboard holder. It's not the glass window that causes items to fade when exposed to the ultra-violet rays of the sun ... it is the UV. Mylar is an inert material.

For a detailed discussion on the effects PVC plastic has on certain chips ... as a suggestion, one can review dozens of prior chipboard posts simply by visiting the archives from a couple of years back and type in the search word - PVC.