You can enable day showing for the previous and next month by #setShowLeadingDates(true) and #setShowTrailingDates(true). A method to enable displaying week numbers is also available (#setShowingWeekNumber()). The foreground color for special weekdays can be changed by #setDayForeground(int DayOfWeek, Color c) - in the example we changed the color for Saturdays and Sundays.
All relevant lines are highlighted. Press the "Run..." button to start the example.