Calendar.IsTodayHighlighted Property

// Create a Calendar that displays dates through
// Januarary 31, 2009 and has dates that are not selectable.
Calendar calendarWithBlackoutDates = new Calendar();
calendarWithBlackoutDates.IsTodayHighlighted = false;
calendarWithBlackoutDates.DisplayDate = new DateTime(2009, 1, 1);
calendarWithBlackoutDates.DisplayDateEnd = new DateTime(2009, 1, 31);
calendarWithBlackoutDates.SelectionMode = CalendarSelectionMode.MultipleRange;

// Add the dates that are not selectable.
calendarWithBlackoutDates.BlackoutDates.Add(
    new CalendarDateRange(new DateTime(2009, 1, 2), new DateTime(2009, 1, 4)));
calendarWithBlackoutDates.BlackoutDates.Add(
    new CalendarDateRange(new DateTime(2009, 1, 9)));
calendarWithBlackoutDates.BlackoutDates.Add(
    new CalendarDateRange(new DateTime(2009, 1, 16)));
calendarWithBlackoutDates.BlackoutDates.Add(
    new CalendarDateRange(new DateTime(2009, 1, 23), new DateTime(2009, 1, 25)));
calendarWithBlackoutDates.BlackoutDates.Add(
    new CalendarDateRange(new DateTime(2009, 1, 30)));

// Add the selected dates.
calendarWithBlackoutDates.SelectedDates.Add(
    new DateTime(2009, 1, 5));
calendarWithBlackoutDates.SelectedDates.AddRange(
    new DateTime(2009, 1, 12), new DateTime(2009, 1, 15));
calendarWithBlackoutDates.SelectedDates.Add(
    new DateTime(2009, 1, 27));

// root is a Panel that is defined elswhere.
root.Children.Add(calendarWithBlackoutDates);

<!-- Create a Calendar that displays dates through
     Januarary 31, 2009 and has dates that are not selectable. -->
<Calendar Margin="20" SelectionMode="MultipleRange"  
          IsTodayHighlighted="false" 
          DisplayDate="1/1/2009"
          DisplayDateEnd="1/31/2009"
          xmlns:sys="clr-namespace:System;assembly=mscorlib">

  <Calendar.BlackoutDates>
    <CalendarDateRange Start="1/2/2009" End="1/4/2009"/>
    <CalendarDateRange Start="1/9/2009" End="1/9/2009"/>
    <CalendarDateRange Start="1/16/2009" End="1/16/2009"/>
    <CalendarDateRange Start="1/23/2009" End="1/25/2009"/>
    <CalendarDateRange Start="1/30/2009" End="1/30/2009"/>
  </Calendar.BlackoutDates>

  <Calendar.SelectedDates>
    <sys:DateTime>1/5/2009</sys:DateTime>
    <sys:DateTime>1/12/2009</sys:DateTime>
    <sys:DateTime>1/14/2009</sys:DateTime>
    <sys:DateTime>1/13/2009</sys:DateTime>
    <sys:DateTime>1/15/2009</sys:DateTime>
    <sys:DateTime>1/27/2009</sys:DateTime>
    <sys:DateTime>4/2/2009</sys:DateTime>
  </Calendar.SelectedDates>
</Calendar>