Why my legos are yellowing if I always have the curtains down?

I always keep the curtains down in my Lego room, and in theory, no light should get in there on its own. So why have some of my figures yellowed while others haven't? I had Marion in a drawer, and she yellowed too. Is there any way to protect them? I'd be devastated if the same thing happened to my Space Iron Man and my Snowtroopers. submitted by /u/Rouble-Branch-150 [link] [comments]