Hello Lahmar,

One possible approach to acheive desired behavior could be if you are using DrawFilter. I`m not sure what is your control into your application, that`s why I made small sample using UltratimeLineView, but you could use the same approach for UltraDatView and UltraMonthView controls

Please take a look at the attached sample for more details and let me know if you have any questions.

Regards

  public class MyDraw1 : IUIElementDrawFilter
    {
        public bool DrawElement(DrawPhase drawPhase, ref UIElementDrawParams drawParams)
        {
            Infragistics.Win.UltraWinSchedule.TimelineView.AppointmentUIElement AppElement = drawParams.Element as Infragistics.Win.UltraWinSchedule.TimelineView.AppointmentUIElement;

            if (drawPhase == DrawPhase.AfterDrawElement && AppElement != null)
            {
                foreach (Appointment app in Form1.CalendarInfo.Appointments)
                {
                    if ((app.EndDateTime - app.StartDateTime).TotalDays > 2)
                    {
                        AppearanceData DrawColor = new AppearanceData();
                        DrawColor.BackColor = Color.Red;
                       drawParams.DrawBackColor(ref DrawColor, new Rectangle(AppElement.Rect.X, AppElement.Rect.Y, 85, 10), new Rectangle(AppElement.Rect.X, AppElement.Rect.Y, 85, 10), true);
                    }
                }
            }
            return false;
        }

        public DrawPhase GetPhasesToFilter(ref UIElementDrawParams drawParams)
        {
            Infragistics.Win.UltraWinSchedule.TimelineView.AppointmentUIElement slot = drawParams.Element as Infragistics.Win.UltraWinSchedule.TimelineView.AppointmentUIElement;
            if (slot != null)
                return DrawPhase.AfterDrawElement;
            else
                return DrawPhase.None;
        }
    }