color polydata (Models) by cell/point component has been implemented by Nicole. We need to figure out how to deal with RGB components.

New code is in the MRML library to support cell and point scalars.
Can you give me an example of an RGB scalar overlay that's not working with the current code base?
(more work on FreeSurfer scalar overlays may lead me to fix RGBA overlay display for multiple scalar fields, not sure on the time line though)

vktMRMLModelNode::CompositeScalars now available, works on point scalars right now.

Should be tested for cell scalars, but has been implemented.

Have a test case for cell scalars, updated the viewer widget.
Now can select scalars from the drop down menu in the Models module display widget and have the display switch between colouring by point scalars and cell scalars.

Implementing the cell and point scalars introduced a problem with scalars on the tractography module's fibre bundle nodes. A work around was checked into the code for the vtkSlicerViewerWidget (if node is a fibre bundle, don't do anything), working to try and find what setting is the culprit.
http://www.na-mic.org/ViewVC/index.cgi/trunk/Base/GUI/vtkSlicerViewerWidget.cxx?r1=4920&r2=4982
To test future fixes:
Modules->Tractography->DisplayLoadSave
Load Tractography button
browse to Slicer3\Modules\Tractography\Testing\TestData\tract_00006_Tensors.vtk
Make sure the display pane has visibility set for lines and glyphs, set glyph type to ellipsoid, colour by FA with the rainbow colour node - should see very colourful tracts.