Welcome to flyertalk bbelass. Your colleague has not many options. Since the airspace is still closed due to the volcanic ash no flights will leave from Frankfurt today. As an Indian citizen your colleague needs a visa to enter Germany and the Schengen area. German authorities don't care if your colleague has a work visa for the US or even a Green Card.

The only thing your colleague is to get in contact with his airline to get some help from them but even they can't do much.