I tried to update XMP info of RAW+JPG files while having set details on the RAW file willing to add the same to the JPG files. However while having preferences set to display metadata in combined view from the JPG I couldn't update from the RAW files (nor on PM 4.5.2 nor after updating to the newest beta). PM ran the update process - taking much time with large amount of images - and can't say for IPTC but none of the color codings were applied from RAW to JPG. Neither in combined view did the color codes of the JPG change, nor in separate RAW and separate JPG view which should (I suppose) allways show the actual status of all files separately.
However setting the display preference to display metadata from RAW in combined view allowed the update function to update the color codes from RAW back to JPG.
I think this is a bug and I would see more use if the update would run effectively regardless of the display preference of the combined view. Or if it is meant to work this way I think a warning should be displayed that the update with current settings won't have the expected effect of updating all IPTC/XMP info - at least not the color coding.