2000 Coloured 50c Proof Discolouration

There are many factors that may contribute to the discolouration of anything you buy from the Mint,Enviroment would be a major factor in many cases,fluctuation in tempature & moisture, as we know extreme tempature changes occur frequently in Australia.
MOR's took the words right out of my mouth in his post,another example would be the 1985 Mint Sets,the yellowing of the plastic in the folders,if someone buys one of the yellow plastic sets now & it's been sold half a dozen times in the period since it's release,would this entitle them to contact the Mint & say their set has discoloured plastic & they want a replacement or credit for another agreed product,again I don't think so !

Other examples would have to be considered seperately on their own merits.
I think the proof sets are more clear cut.
Environment is pretty much irrelevant to the proof sets we are discussing as they are sealed.

Couldnt condensation still occur inside the packaging if the temperature change quickly?

Thanks Enworb & ozcoins

& yes I do believe even though the proof set are sealed,temperature changes would have some affect on these sets,even if it is only slight but happeneed several times over a period of time until it becomes significant.