Hello,
I also got some help elsewhere, and I managed to do it as follows:
I just opened a copy of my ppproject and relinked there the existing sequence in the timeline to the color files, after I renamed them (so they had not the same name as the outlines)
then I copied this sequence into the original ppproject, after I had imported the folder with the renamed color-files in it,
and now I have the 2 identical sequences, referring to 2 different image-folders in my ppproject,
that is what I needed.
Thanks anyway,
Geert