The inability to set the background in native iOS apps to a color scheme that works well for night time or dark places is one of my major gripes too. I do a lot of astrophotography and I like to take notes with the Notes app. But opening an app like Notes in the dark is quite a shock to my eyes and will mess up my night vision for quite a few minutes thereafter. Even indoors while watching TV at night with the lighting dim causes a huge glare to the eyes. The same with safari and many other iOS native apps. It would be really great to be able to change the color schemes, and it would not be that difficult for Apple to implement, but they simply don't won't to. Apple can be to artsy-fartsy. They treat their UI as though it was a piece of artwork that cannot be changed. I wish they would get over themselves and go more with usability than looks.