Hello PMac,

In order to change the fill color of an appointment in the XamSchedule (for example when using XamOutlookCalendarView), an approach I can suggest you is to simply get the respective Path element of the AppointmentPresenter element (visual representation of the Appointment) and set it's Fill property.

For example:

XAML:

<ig:XamOutlookCalendarView.Resources>
    <Style TargetType="{x:Type igPrim:AppointmentPresenter}">
        <EventSetter Event="Loaded" Handler="AppointmentPresenter_Loaded" />
    </Style>
</ig:XamOutlookCalendarView.Resources>

Code-behind:

void AppointmentPresenter_Loaded(object sender, RoutedEventArgs e)
{
    var appointmentPresenter = (sender as AppointmentPresenter);
    var activitySubject = (appointmentPresenter.Activity as Appointment).Subject as string;

    if (activitySubject == "HR Consulting")
    {
        var mainGrid = Utilities.GetDescendantFromType(appointmentPresenter, typeof(Grid), false) as Grid;
        var innerGrid = Utilities.GetDescendantFromType(mainGrid, typeof(Grid), false) as Grid;
        var borderPath = Utilities.GetDescendantFromType(innerGrid, typeof(Path), false) as Path;
        borderPath.Fill = new SolidColorBrush(Colors.DarkOrange);
    }
}

I have attached a sample application, that uses the approach from above.

If you have any further questions on the matter, please let me know.