function annotateCalendarEvents() {
  const date = new Date()

  // get active user's domain name
  const userDomain = Session.getActiveUser().getEmail().split("@")[1]

  // see colors here https://developers.google.com/apps-script/reference/calendar/event-color
  const colorString = ("11")

  /*
  get Calendar Events for today, fetch guest list for each event, parse guest's domain
    compare user's domain with guest's domain, if doesn't match, change event color
    */

  const events = CalendarApp.getDefaultCalendar().getEventsForDay(date)
    .forEach(event => {
      const participants = event.getGuestList().forEach(guest => {
        if (guest.getEmail().split("@")[1] !== userDomain) {
          event.setColor(colorString)

        }
      })

    })

}