On Android internal SD card, replace:
/data/org.xbmc.kodi/files/.kodi/addons/skin.aeon.nox.5/backgrounds/default_bg.jpg
with another JPG of 1920x1080
This will repace the default Gravity background with another JPG for all Kodi screens.
.kodi is a hidden directory
Copy can be done simply with MiExplorer or something similar.
