
Originally Posted by
stjarna
The yellowing of the bubble is the result of a chemical degradation/breakdown in the bubble itself. Storing a carded figure/giftset in total darkness can still result in a yellowed bubble. Mattel (and all of its global manufacturing plants) used cheap plastic (as opposed to collector-minded archival plastics, lol). It is absolutely inevitable that your bubbles will yellow. Enjoy it while it's clear and then move on.
As a side note, it is not uncommon for figures from sealed cases to have yellowed bubbles.