Surface Pen LED Light Microsoft filed Patent
The Patent was filed in February 2017 which describes a stylus for touchscreen devices
The most basic feature would be an LED in the tip which would reflect the current color of the ink which would be applied when the pen is being used to write. Thus the user can recognize which color he is currently using, without having to reassure himself on the screen elsewhere.
The LEDs to be integrated with the stylus could also be used elsewhere to serve as a sort of notification to inform the user about incoming messages, status updates or emails. It will also indicate the battery level used in the stylus.