It is better to choose a monotonous color palette, because too rich and contrasting design will irritate your eyesight. Excessively light, bright or completely black desktop wallpaper will interfere with the comfortable use of the smartphone without additional strain on the eyes. To find a nice wallpaper for your eyes, I suggest you look here
https://rare-gallery.com/ . Here is a great selection of quality wallpapers for your desktop, and most importantly they will not harm your eyesight.