As we reported, Google's Android P broke cover yesterday with a developer preview released to users of the Pixel series of devices. The update came with a number of changes including improvements to security and notifications. Unfortunately for some enthusiasts, Google's improvements to security also came with a hidden cost, the loss of custom theming functionality. For context, in Android 8.0 Oreo, Google added support for an Overlay Management Service in stock Android, allowing devices running Oreo to be themed. This feature was not exposed to consumers, and only enthusiasts who used a series of ADB commands were able to take advantage of the change.
The developers of the Substratum theme engine created an Andromeda framework for Android Oreo which allowed users of the mod to apply custom themes to their devices relatively painlessly. Users could give themselves a dark theme in apps, the notification centre, change app icons and so much more. Effectively, this made Android more customisable for users who had the desire to put in the work.
With Android P, Gooogle has changed the behaviour of the OMS, and now only allows pre-authorised overlay themes to run. Users are no longer able to install Substratum overlays due to the change. This change extends as well to rooted users, but not users of custom ROMs who can change the way Android itself runs on their device.
Google will still let manufacturer custom overlay tools and themes like those supplied by Samsung, Sony and Xiaomi work. Custom themes, absent a change of heart from Google, appear to be dead for now.
via XDA Developers