Supposedly white bricks yellowing is only a problem with bricks made before they switched to a new plastic in the mid-2000's. But having just built a massive Saturn-V mod MOC, I took the Saturn V built directly from the parts that came in the set, bought from Lego, and now the entire thing's horribly yellowed. Meanwhile recently only some specific bricks from Lego's modular buildings diner went fully yellowed in what seems to only have been a year or two. While the diner was on display on the main floor of the house, the rocket has been sitting in a dark closet for at least the last six years! (Hasn't been opened in long enough that it smelled when I did open the door.) It's possible the Saturn V had yellowed before that point though.
Which brings up the question - with "last several years" bricks, is there any way to stop them from yellowing, or do you just need to completely remove them from any possible sunlight (or not display them in a room with any windows), or is there a way to safely display them in a house full of windows on the west side?
Thanks.