变文本element的背景色

            ITextElement  ele = new TextElementClass();
            ele.Text = "大学四年生活";
            IPoint point= new PointClass(){  X=e.mapX,Y=e.mapY};
            (ele as IElement).Geometry =point;
            IFormattedTextSymbol formatted = new TextSymbolClass();

            IRgbColor rgb = new RgbColorClass();
                rgb.Red = 255;
                rgb.Green = 255;
                rgb.Blue = 0;

            ISimpleFillSymbol sfs = new SimpleFillSymbolClass();
            {
                sfs.Color = rgb;
            }
            IBalloonCallout pCallout = new BalloonCalloutClass();
            (pCallout as ITextMargins).BottomMargin =3;
            (pCallout as ITextMargins).LeftMargin =4;
            (pCallout as ITextMargins).RightMargin =4;
            (pCallout as ITextMargins).TopMargin =3;

            pCallout.Style = esriBalloonCalloutStyle.esriBCSRectangle   ;
            pCallout.Symbol = sfs;
            IRgbColor rgb1 = new RgbColorClass();
            rgb1.Red = 23;
            rgb1.Green = 34;
            rgb1.Blue = 254;
            ITextBackground back = pCallout as ITextBackground;
            formatted.Background = back;
            formatted.Color = rgb1;
            ele.Symbol = formatted as ITextSymbol;
            axMapControl1.ActiveView.GraphicsContainer.AddElement(ele as IElement, 0);
            axMapControl1.ActiveView.PartialRefresh(esriViewDrawPhase.esriViewGraphics, ele, null);