C# 如何为Outlook AppointItem的类别着色

我正在使用office.NET框架在Outlook中创建约会。创建约会的代码如下所示：

    private void createCalendarEvent(DateTime start, DateTime end, String dept, String subj, String subjType, String room)
    {
        AppointmentItem apt = (AppointmentItem)OLapp.CreateItem(OlItemType.olAppointmentItem);

        apt.Start = start;
        apt.End = end;
        apt.Subject = subj + " - " + subjType;
        apt.Body = "Subject: " + subj + " (" + subjType + ")"
                + "\nDepartment: " + dept
                + "\nRoom: " + room
                + "\n\nCreated by " + this.Text
                + "\n On " + DateTime.Now.ToLongDateString() + " At " + DateTime.Now.ToLongTimeString();
        apt.Location = room;
        apt.Categories = subj;
        apt.Save();
    }

这很好，但我设置的类别没有与之相关的颜色。我希望outlook中的约会根据类别集以不同的颜色显示。有什么方法可以手动设置类别颜色吗？或者更好的方法，让框架自动为我选择类别颜色？

答案涉及类别。具体来说，这里有一些代码（VB.net，但很容易转换）将创建一个暗橄榄类别：

Private Shared ReadOnly CATEGORY_TEST As String = "Custom Overdue Activity"

' This method checks if our custom category exists, and creates it if it doesn't.
Private Sub SetupCategories()
    Dim categoryList As Categories = Application.Session.Categories
    For i As Integer = 1 To categoryList.Count
        Dim c As Category = categoryList(i)
        If c.Name.Equals(CATEGORY_TEST) Then
            Return
        End If
    Next

    categoryList.Add(CATEGORY_TEST, Outlook.OlCategoryColor.olCategoryColorDarkOlive)
End Sub

类别颜色可以在Outlook中设置，也可以在代码中创建类别时在上面的代码中设置