With Android 6.0 Marshmallow and the third developer preview now out for anyone with a supported device and the desire to flash the software, there will likely be a small landslide of new features or small tweaks to pay attention to. One of these changes has to do with the system UI tuner which Google actually introduced with the Android M Dev Preview 2 a couple of months back. While the system UI tuner itself is not new, there is now a new way to activate the functionality so it's enabled on your device. It's also worth mentioning that it may not be as straightforward as before, so if you're one who likes to customize and tinker a little bit you'll want to take note of how to turn this feature on.
When you think about it enabling system UI tuner is actually quite simple, and all you have to do to get things going is drag down the notification shade. Once you do this if you divert your attention to the system tray up top you'll see the tiny gear icon which takes you to the settings menu upon tapping on it. This is also nothing new, but instead of tapping on the gear icon if you now tap and hold it down, the gear icon will begin to spin and then enter into the settings menu followed with a popup message that states "Congrats! System UI tuner has been added to settings."
What this does is enable the system UI tuner functionality rather quite simply and quickly. You can also utilize this method to disable the system UI tuner feature in the same manner. When system UI tuner is enabled you'll notice the new little wrench icon next to the gear icon for settings. Same as before, tap and hold on the gear icon until you see it start to spin, and then you'll be taken into the settings menu and greeted with a message which asks you if you'd like to remove system UI tuner from the settings menu. That's all there is to it. Now you can turn it on more easily at your leisure for customizing the status bar icons and the quick settings toggles among other things. You can also now download the wallpapers what looks like all of the Android Marshmallow wallpapers.