The  latest trend for sorting folders on the iPhone home screen is to use  duotone wallpapers with one half darker than the original image.

With  this shortcut you can generate this effect in a few taps, choosing the  original image, the density of the effect and the position you want to  assign.

The image is corrected automatically without having to open the "wallpapers" option from the iPhone settings.

All you have to do is set the final image in the screen, just like you do in the wallpapers option.