Python: ColorBy(<handle>, None) doesn't work

Hi all, for an openFOAM case I a creating roundabout 1000 slices in a geometry. To distinguish them visually, I want to color them iteratively [red, green, blue]. In PV 5.0.1, my code worked fine: Let slice_display be the object handle, then

ColorBy(slice_display, None)
slice_display.DiffuseColor = [1.0, 0.0, 0.0]  # red

worked. But: In PV 5.4.0, the ColorBy argument None doesn't work. Even a trace doesn't show the desired line of code.

Steps to reproduce:

1. Download minimal working example -> MWE_meshed.zip
2. Load case into PV.
3. Run execute_script() in MWE_colorBy_error.py