This app makes white colors look better

Looking at bluish light a lot can cause medical problems, which is why some phones have a "reading mode" to make the background more yellow. It's for your own benefit if you're on the phone a few hours a day.
 
Looking at bluish light a lot can cause medical problems, which is why some phones have a "reading mode" to make the background more yellow. It's for your own benefit if you're on the phone a few hours a day.

Oh so that's why it's yellow on purpose