title: vtkLookupTable specifing colors with opacities
body: <p>I am trying to use a vtkLookupTable in order to set the colors for my mesh. I started with vtkColorTransferFunction which worked fined except that it does not enable me to set opacities for various colors. 
  vtkLookupTable offers this opportunity, but I am having problems to get it working.</p>
  
  <p>My vtkPolyData have scalars value set that determine the color they shall get. Overall 7 values, set with the scalars 0 to 6. </p>
  
  <p>My vtkLookupTable looks like this:</p>
  
  <pre><code>vtkLookupTable lut = new vtkLookupTable();
      lut.SetNumberOfColors(7);
      double opacity = 0.3;
      lut.SetTableValue(0, 0, 0, 1, opacity);
      lut.SetTableValue(1, 0, 1.0, 0, opacity);
      lut.SetTableValue(2, 0.6, 1.0, 0.0, opacity);
      lut.SetTableValue(3, 1.0, 1.0, 0.0, 0.7);
      lut.SetTableValue(4, 1.0, 0.8, 0.0, opacity);
      lut.SetTableValue(5, 1.0, 0.4, 0.0, opacity);
      lut.SetTableValue(6, 1.0, 0.0, 0.0, 1);
  </code></pre>
  
  <p>If I use a vtkColorTransferFunction with the same values (just no opacity) it works. Anyone any idea why this is not working? I should be same? </p>
  
  <p>Thanks for help.</p>