The upcoming Ulefone Future model just received another extra function with the System UI Tuner for Android 6.0 Marshmallow, which should allow the users to tweak a bit the UI. Nothing major, but ...

Hidden System UI tuner Customize your Android’s status bar and notifications using the System UI Tuner. Long-press the Settings icon in the Quick Settings menu until it spins.

If your Android phone has its own dedicated System UI app, you can clear its cache by following these steps: On your Android device, navigate to the Settings app.