C#: Two different highlight colour on zoom in design file changes to default highlight colour, how to retain both highlight colours?

I'm working on an application that uses Bentley Microstation for design purpose. So this application references the Microstation, and there is a program to start  Bentley Microstation interface from the application.

I open a design file and i highlight few element in design file like shown in below code:

                MicroStationDGN.Application app = _app;
                MicroStationDGN.ApplicationClass ustn = new MicroStationDGN.ApplicationClass ();

                Element ele = default(Element);
                
                //highlight for modified elements
               
                    DLong Id=default(DLong);
                    
                    Id.High=0;
                    Id.Low=Convert.ToInt32("35754");                    

                    //Change highlight colour to RED
                    SendKeyIn("SET HILITE RED");


                    ele=(Element)(app.ActiveModelReference.GetElementByID (ref Id));
                    ele.IsHighlighted=true;


                   //Change highlight colour to BLUE
                    SendKeyIn("SET HILITE BLUE");             

                    Id=default(DLong);
                    
                    Id.High=0;
                    Id.Low=Convert.ToInt32("37664");                                      


                    ele=(Element)(app.ActiveModelReference.GetElementByID (ref Id));
                    ele.IsHighlighted=true;


So the few elements are highlighted in BLUE and few in RED.

When i zoom the design file to check the elements, all the highlighted elements are highlighted in one colour, in the above case BLUE.

I tried to lock each highlighted elements but it dint work as shown below:

            SendKeyIn("change lock");            

How can i retain both the colours in the design file?