Hey guys,I just finally found a way to make my Moto G4 Plus completely look black with Dark Material theme.
Prerequisites
1. Rooted Device
Step 1 : Install Busybox on rails from google play store and install busybox (Grant supersu permissions) (if busybox not installed already)
Step 2 : Install "Layers Manager" from play store
from this you can choose hell lot of customisable themes
Step 3 : Install whatever the theme you like, I've installed "Dark Material for layers" which will turn my moto g4 plus completely black and save power.
Now reboot your device and done!
Note: If you cannot uninstall any theme after installing don't panic, just go to /Vendor and delete all the apk files installed