Correct, volume rendering transfer functions do not affect probing. If you probe a scalar volume then you can apply transfer functions on the values by a couple of lines of Python code (get the array and run each value through the color transfer function).
We played with this a bit on RGB volumes (cryosection data) and the result was pretty disappointing. It was not surprising, because segment surfaces tend to have fairly uniform color (non-uniformities are usually under the surface). Therefore, we did not continue exploring “saving volume rendering as colored surface”.
If you have examples of surface rendering beautifully displaying volume rendering results then we can revisit this. Can you share a few examples that shows the volume rendering and colored surface rendering?