aospUI Gray theme matches exactly the colors and user interface that Google made for Android N second preview, extended on more apps, it's "the old" O/Pixel Dark Mode.
The theme installs through an app that this app will link you to, where you will have to buy an add-on made by Substratum developers).
The theme supports:
Samsung, AOSP based, OnePlus and Google systems
from Nougat, up to Pie*.
*root needed on Pie, except on Samsung where you can use Synergy or Andromeda
It is recommended to connect your phone to adb on your PC before installing the themes unless you're rooted, because with adb you can recover your phone from eventual bootloops without wiping.
Many manufacturers' ROMs aren't guaranteed to be compatible (the more different they are from AOSP or Google ROMs UI, the more they're likely to not be compatible.
In case you end in bootloop flash the rescue zips that you find in /sdcard/Substratum/, if you have custom recovery, and ask for refund, also by e-mail if you need.
Themed elements list (70+ apps): http://txt.do/dlvhx
Thank you all for supporting my work. :)