While Google may not have introduced official support for themes in Android 8.0 Oreo, it did lay the underlying groundwork for themes. Even better, you will be able to apply themes to your Android device without having to root it first, which is usually the case right now.
Thanks to the hard work of Sony on Overlay Manager Service (OMS) which has made its way into Android 8.0 Oreo, it is possible to theme an Android device running Oreo without bothering with root access. In fact, since Substratum themes — the current choice of theming for third-party ROMs — is based on OMS, it will work under Android Oreo without any kind of modifications.
The only problem here was that installing Substratum theme itself required root access. Well, there is now a rootless theme solution in works from the developers behind Substratum. The process is a bit hacky though. It requires providing elevated privileges through a script to Substratum themes so that they can be installed. This involves connecting your phone to a PC and running an elevated shell of ADB.
While you will be able to install Substratum themes without root access using this method, there’s a major catch: the elevated privileges are lost when you reboot your device. This means you will have to connect your phone to your PC again and grant it the necessary privileges if you wish to change, remove, or install a new theme.
If all this has you excited, the developers behind this whole project are promising to release a compatible version of Substratum theme manager for Android 8.0 Oreo for the Nexus 5X, Nexus 6P, and the Pixel/XL within a week from now.
If you are excited about Substratum theme support coming to Android 8.0 Oreo, check out the detailed write-up on it over at the source link below.
[Via XDA]