[vtkusers] how to color a vtkStreamTracer with velocity- results?

[McCoy]

hi all,

i guess my actual prolblem is pretty simple, but at the moment i'm
stuck:
i have been calculating streamLines for a while. till now i used
vtkStreamLine for that, now i'm trying to switch my code to
vtkStreamTracer. but how do i map the velocity to the tracer? in
vtkStreamLines there was the flag
  sl->SpeedScalarsOn()
but thats gone with the tracer.
i tried vtkAssignAttribute as shown in the StreamTracer.tcl example,
but the generated lines stay grey. any ideas, what i'm missing?

thanks in advance....
Joseph