Most of the power Android users swear by rooting their phones and opting for custom ROM’s. The most common reason for this is that the users want to have more control and more options to customise their device without any restrictions. In fact, it was this very preference that gave rise to the Cyanogen Mod and the entire mod community. System wide theme support is one of the reasons why people prefer to root their Android phones. That being said rooting Android is not for everyone and a large chunk of people prefer to use their phones in stock.
Substratum (theme engine) has been working on a system-wide theme and now it has finally introduced a full-system-wide theme for Android Oreo without requiring root access. The support is going to change a lot of things for Android Oreo users. To begin with theming of the Android Framework and Android System UI will extend custom themes to any third party application. Moreover, it will also allow users to modify other stuff like a status bar or even use a centre -clock mod.
Substratum already has a bunch of themes available that support the framework, moreover, they also have an active community on Google+ and a dedicated thread in XDA forum. The theme support has been on the cards and the only missing piece of the puzzle was the public API. The Sony RRO was added to the Android Open Source Project (AOSP) in the Marshmallow and nothing happened until now.
The engineers at Sony Mobile have revamped the Runtime Resource Overlay (RRO) theme and now it’s known as Overlay Manager Service (OMS.) The AOSP was finally accepted in the final Android 7.1 release but the non-Sony users were left with no options but to root their phones. Things changed drastically when Sony realised that an existing Subrtatum-supported theme would be fully functional on Android Oreo without the need for root access. In fact, it was this very workaround that was used by other apps like Helium and Greenify.