public bool IsCustomColor {get; set;}

{
  // Note: call within QueuedTask.Run()
  {
    var variable = voxelLayer.SelectedVariableProfile;

    //Change the color of the first surface for the given profile
    var surface = variable.GetIsosurfaces().FirstOrDefault();
    if (surface != null)
    {
      if (voxelLayer.Visualization != VoxelVisualization.Surface)
        voxelLayer.SetVisualization(VoxelVisualization.Surface);

      //Change the iso surface voxel value
      surface.Value = surface.Value * 0.9;

      //get a random color
      var count = new Random().Next(0, 100);
      var colors = ColorFactory.Instance.GenerateColorsFromColorRamp(
        ((CIMVoxelStretchRenderer)variable.Renderer).ColorRamp, count);

      var idx = new Random().Next(0, count - 1);
      surface.Color = colors[idx];
      //set the custom color flag true to lock the color
      //locking the color prevents it from being changed if the
      //renderer color range or color theme is updated
      surface.IsCustomColor = true;

      //update the surface
      variable.UpdateIsosurface(surface);
    }
  }
}

{
  var variable = voxelLayer.SelectedVariableProfile;
  //Change the color of the first surface for the given profile
  var surface = variable.GetIsosurfaces().FirstOrDefault();
  // Note: call within QueuedTask.Run()
  {
    if (surface.IsCustomColor)
    {
      surface.Color = variable.GetIsosurfaceColor((double)surface.Value);
      surface.IsCustomColor = false;
      //update the surface
      variable.UpdateIsosurface(surface);
    }
  }
}