Nexus 6 seems to be full of surprises as a new secret feature was recently discovered. It appears that the device has a hidden LED that can be put to use with root notifications. The phone also has ambient screen mode, which means notifications are displayed when they come in in a rather ingenuous way.
It also has a built-in physical LED positioned at the top speaker/earpiece and it can produce red, green and blue light. Some apps can even use it to display notifications but only if your device is rooted. The device doesn’t even have to be plugged in to do its magic this way.