I synchronize my calendar files between home and office using unison, and for any calendar file that is changed, the color assignment is lost. This behavior can be reproduced generally by replacing/editing an .ics file outside of korganizer.

Reproducible: Always

Steps to Reproduce:
1. Add a trial event in a calendar file using korganizer
2. Edit that calendar file with an outside tool, removing the trial event
3. Overwrite calendar file with the edited version.
Actual Results:  
Upon replacing a largish .ics file, one sees in korganizer how first all entries belonging to that file are  removed (rather slowly, even though I have a fast workstation), and then how they are added back in with a different colour.

Expected Results:  
Korganizer should show the replaced calendar with the color assignment that belonged to that file.

I checked in .kde/share/config/korganizerrc, and noticed that the many times I have by now corrected the color assignments has led to a very long list of "akonadi:?collection\x3d...=....", so it looks like that akonadi starts a new collection whenever a file is changed, and that korganizer, not surprisingly, doesn't know that really this collection reflects the same file, just with updated content.