Apple does make the top part of the screen a bit darker. That's so on the lock screen the time and date stand out more. Or "pop". It makes light colored wallpapers look bad. But I don't even see that in the screenshot provided. The coloring seems to have improved recently. I don't see as much darkening as I used to. The text time/date is supposed to change from white to black when a light colored wallpaper is used. But it hasn't worked all that well until iOS 9. It has improved. But when a light wallpaper was used, rather than it change to black text, it would darken the screen so the white text could be seen better. I just did testing, and didn't see any darkening. They apparently have done a better job with changing the text color with the wallpaper color. The OP may still see this screen darkening.