public double Transparency {get; set;}

{
  //Update an element's transparency using the CIM.

  //Note: Must be on QueuedTask.Run

  // Reference a element by name
  GraphicElement graphicElement = layout.FindElement("MyElement") as GraphicElement;
  if (graphicElement != null)
  {
    // Modify the Transparency property that exists only in the CIMGraphic class.
    CIMGraphic CIMGraphic = graphicElement.GetGraphic() as CIMGraphic;
    CIMGraphic.Transparency = 50; // mark it 50% transparent
    graphicElement.SetGraphic(CIMGraphic);
  }
}