One possible approach to acheive desired behavior could be if you are using FillScenGraphe event and Polyline Primitive.  For example

private void ultraChart1_FillSceneGraph(object sender, Infragistics.UltraChart.Shared.Events.FillSceneGraphEventArgs e)

        {

            List<Polyline> originals = new List<Polyline>();

            List<Polyline> fisrtStageLsit = new List<Polyline>();

             foreach (Primitive pr in e.SceneGraph)

            {

                if (pr.GetType() == typeof(Polyline))

                {

                    DataPoint[] dtpFirstStage = new DataPoint[((Polyline)pr).points.Count()];

                    int k = 0;

                    foreach (DataPoint dp in ((Polyline)pr).points)

                    {

                        originals.Add((Polyline)pr);

                        if (k < 4) dtpFirstStage[k] = dp;

                        k++;

                     }

                    ((Polyline)pr).lineStyle.DrawStyle = LineDrawStyle.Dot;

                    ((Polyline)pr).PE.Fill = Color.Yellow;

                    ((Polyline)pr).PE.StrokeWidth = 3;

                    Polyline fisrtStage = new Polyline(dtpFirstStage);

                    fisrtStage.PE.Fill = Color.LightBlue;

                    fisrtStage.PE.StrokeWidth = 4;

                    fisrtStage.lineStyle.DrawStyle = LineDrawStyle.Solid;

                     fisrtStageLsit.Add(fisrtStage);

                }

            }

            if (fisrtStageLsit.Count > 0)

            {

                foreach (Primitive item in fisrtStageLsit) e.SceneGraph.Add(item);

            }

         }

Please take a look at the attached sample for more details