Any faction only has a single home system and can be retreated from all others, and colonies are no exception to that.
Of course if you retreat one of the other three factions quickly enough, there'll no longer be enough factions in the system to start another retreat until and unless someone else expands in - unlikely, in many parts of the new bubble.
(There have been some reports of retreats failing unexpectedly in colonised systems, but enough of them seem to work normally on a range of factions that this is probably just a weird bug)