You would need to do some software programming for this. Search arduino OTG RGB LED. You can set the color of an RGB LED using a phone's OTG port (uses the micro USB as a host) and sends serial commands to an arduino. At this point you might need to make a mod for the android OS that creates a virtual notification LED as part of the phone's hardware, and an app that spits out serial commands over USB based on what this virtual LED is doing.
You would need to do some software programming for this. Search arduino OTG RGB LED. You can set the color of an RGB LED using a phone's OTG port (uses the micro USB as a host) and sends serial commands to an arduino. At this point you might need to make a mod for the android OS that creates a virtual notification LED as part of the phone's hardware, and an app that spits out serial commands over USB based on what this virtual LED is doing.