I just found a Pandoran Lair well within a zone that was mist-repelled. This area had been mist free for in-game weeks. I only discovered the location after defending a haven in the same mist-free zone. Before investing in upgrading the base, I thoroughly re-scanned the area with the proper tech to reveal Pandoran colonies. Nothing was revealed. Again this was in-game weeks prior to my finding this lair.
It is my understanding that colonies are only established in mist areas, not mist free areas…