Theme customization is important if you want to get rid of the "Hero" wallpaper for new users.
This script will determine the Operating System and copy either the Win7.theme or the Win10.theme to Custom.theme (in this directory). Set the Theme file to %ProgramData%\OSConfig\Theme\Custom.theme in Group Policy
Windows 7 Aero Theme file with the Wallpaper entry removed
Windows 10 Aero Theme file with the Wallpaper entry removed