Before and after leaving new 3ds LL on for nearly a full week

I bought it from Mercari JP knowing that it would be a bit yellow on the bottom screen so did what I saw suggested here to fix it. It’s definitely improved quite a bit.

Now I’m starting to want to trade for my more ideal color version of pearl white, but not entirely sure how to go about it safely. So far the only thing I’ve done is leave it open to correct the yellowing.