改变feature的颜色怎么无效?

<P>一个层中都是点feature,用3D符号显示,我现在要改变其中一个feature的颜色,不用管什么feature属性,就是改变这个feature的显示颜色.怎么不行啊,我把代码贴出来麻烦大侠帮我看看啊</P>
<P>      Dim pFeatLyr As IFeatureLayer<BR>      Dim pGeoFeatLyr As IGeoFeatureLayer<BR>      Dim pFC As IFeatureCursor<BR>      Dim pFeat As IFeature<BR>      Dim pLayer As ILayer<BR>      Dim pPtSymbol As IMarkerSymbol<BR>      Dim pSRenderer As IFeatureRenderer<BR>      <BR>      Dim pRgbColor As IRgbColor<BR>      Set pRgbColor = New RgbColor<BR>      pRgbColor.Blue = 0<BR>      pRgbColor.Green = 0<BR>      pRgbColor.Red = 255<BR>      <BR>      Set pLayer = SceneControl1.Scene.Layer(0)<BR>      Set pFeatLyr = pLayer<BR>      Set pFC = pFeatLyr.Search(Nothing, True)<BR>      Set pFeat = pFC.NextFeature<BR>      Set pGeoFeatLyr = pFeatLyr</P>
<P>    <BR>      Set pSRenderer = pGeoFeatLyr.Renderer<BR>      Set pPtSymbol = pSRenderer.SymbolByFeature(pFeat)<BR>      pPtSymbol.Color = pRgbColor<BR>      <BR>    <BR>     SceneControl1.Scene.SceneGraph.RefreshViewers</P>
<P>运行不报错,但没有什么反应.</P>