Ye Olde Inn

Has anyone else had their unpainted 'white' miniatures start to go a odd shade of yellow after being in storage for awhile?

Yeah, that's normal.

No cure? (Besides a white undercoat that is).

I don't think so. How hard is the plastic of your figures? There are variants, too, and I'd go with the assumption that the softer ones will yellow sooner. But that's talking put of my ass, really. I've never bothered, cause I plan on painting them at one point.

Yeah I'm probably being a wuss after last painting fascoe, may have to give it another go somewhen.

I hereby encourage you to do so.
Priming, painting and varnishing seven shades of *lemony goodness* out of a mini willl stop the yellowing, to the best of my knowledge.
There are many threads here dealing with painting and showing off painted minis.

even if you only get down some basic skills like me, a set of painted mini's looks so much better at the game table than unpainted mini's

my mini's won't win any competitions but I couldn't tell you if my undead are yellowing as they are painted

I personally LOVE the yellowed figures, they look more bony and undead. I got a few of the UK style undead figures that were pure white, and now they don't match. How to make them "yellow" without painting? I don't know, short of the passage of time..

But I know with other types of plastics, you can put them inside a clear plastic bag full of Hydrogen Peroxide (the kind sold at drug store for purportedly for cleaning wounds) and leaving it in the window sill for a couple of sunny days and that brightens them up. The yellowing affect (as in say, vintage Kenner Star Wars figures) is caused by the reaction of Bromine (a flame-retardant chemical) with light and oxygen over time if memory serves. It might work.

So for now I just have to pretend that these are just "fresher" mummies, skeletons, etc.