The colors on the chip are made by mixing colorants with the molding material... plastic, and sometimes some clay. The colors will come to the surface naturally. If they are in play, the color transfers to the players hands, the felt, and somewhat to other chips. It's natural, and for the purpose they serve, not often a problem.

If you store the chip in contact with something for a long time, the color will naturally transfer to the other surface. If it's in a plastic page, the clear plastic will show some of the color. The bleeding isn't speeded up by the kind of plastic in the holder, whether it has PVC and plasticizers in it or not.

Some of the colorants will "bleed" more than others. Some of the older chips had a red color that bled to adjacent areas of the chip. This happens whether the chip is in a holder or not.

Hard plastic doesn't conform to the surface of the chip and consesquently picks up less of the color from the chip. Air-tite holders, for instance, have a hard surface, and it's not forced against the chip so you will seldom see the colors on the inside of the air-tite. The chips still bleed, though; it's just not obvious. The PVC pages that are more flexible have plasticizers added. This allows them to stretch a bit and conform more closely to the chip surface so you see more of the transferred color.

I have used flexible PVC pages to hold my chip collection for more than 15 years. It think it works fine. Some collectors feel differently, particularly those who have collected coins. The plasticizer in the PVC definitely causes problems in reacting with metal coins. That's a different situation than with plastic chips.