One of my biggest issues with Android Lollipop was the lack of customization. That was one of the main reasons I was using Chroma ROM. I was able to customize the quick settings toggles to my liking and I could theme my device. It seems that Google has definitely listened to its fan base, as the Android M developer preview includes both of those features.
When looking through the device, the new features are hard to find, and that is because it is hidden inside the developer options. Who would have thought? Hiding inside the developer options are the ability to choose between a Light, Dark, and even Automatic theme. So far, this only includes the settings and not notifications, but I wouldn’t be surprised if the dark theme reached out further in later updates. It would truly be great if Google employed a full theme engine, but we won’t know until the final build is released in Q3.
On top of the ability to change the device to a dark theme, you are now able to customize the quick settings inside the notification shade via ‘SystemUI Tuner’. Once that is enabled, it is on the bottom of the settings list, and you are able to drag on drop quick setting toggles.
The SystemUI Tuner has the potential to add a lot of features to Android as an operating system as a whole. I could see it as a feature that would give users the ability to customize their device more without root privileges.
To enable both or either of these features, you need to go to the your settings, about phone, then tap build number seven times. That will enable developer options.