I accidentally mined some ore near a Free Colonists station and they became Unfriendly towards me. This is extremely inconvenient as they seem to own most of the space stations in the universe. It took hours to get back up to neutral because there are almost no ways to gain Free Colonists standing. Supposedly they are enemies to the pirate faction but killing or destroying pirate stuff does not give Free Colonists standing. The only thing that worked was to do a mission to destroy pirate structures and get a credibility seal.
Hm.. did you kill/destroy Pirate property on planet or in orbit or both? Maybe consider this worth a bug report if it worked on only one or neither playfield.
If you check the Empyriopedia in your PDA in game, the only way to gain reputation with the Free Colonists is to kill predators in their territory in the same way as with the Talon. The problem is, the Free Colonists in v1.5 have no territory - even in their own collection of systems bubble ... therefore there is no way to gain reputation with them that does not involve alienating another faction.
[EDIT] Unfortunately, with what I'm saying here below, I have confused the Colonists with the Trader's Guild, so my advice must go in the trashbin...I'm very sorry, this also means that NO Colonist territory has ever been discovered (going by other threads which I did a research for.) --------------------------- Wrong: In 1.4 on neutral or unclaimed planets I have seen Colonist territory marked in white on the map, I did hunt predators and so increased my rep. Now I don't know if these territories still exist in 1.5, but I see hardly a reason why they should have been removed, so move in unclaimed territory to increase your rep with them.