All lights can yellow- UV is bad obviously, but ambient light (i.e. from an electric lamp or overhead lights) will yellow a ball as well, and can't really be blocked out by UV protection. It's just an unfortunately truth of life- things fade.

Either you store it in the dark where it's safe, or you store it out where you can see it. And since the point is to display and see items, I think the answer to that is a no brainer. To each his own though.