Here's the reverse of the chip i posted earlier asking for an ID. As you can see the PVC's in the flip have picked up the color and imprinted it back onto the chip:

This happened several years ago. As a Rule of thumb I toss any suspect PVC flips away. Bear in mind that PVC Slime, as it's called, can transfer to your other chips, especially CIC ones.

It's best to make sure you are using non-pvc flips and pages, or just use air-tites.

"If the flip is flabby, throw it out. If the flip is crisp, save it.

(...and yes I know there are two pieces of big ass lint in the ring!)