Since the exos for this are rare, possibly a fun alternative for in between - an augment that when aimed at a planet and hit - only rentals allowed, and World Control would allow owners to not allow this on their planets (augment just wouldn’t fire if aimed at a non-eligible world, wouldn’t lose it) - turns that world color cycling for a period of an hour.
This should NOT be an easy recipe to craft, require some real grinding, but maybe not with special exo or event stuff. A few recipes catering to different playstyles - like, 20 of each creature trophy, or 100 of each refined regular gem, something like that. An end game activity.
It would give something for people to gather for, give more chances to get colors that can’t be set on rentals. Stimulate some parts of the economy for the ingredients required for the recipes, while getting more blocks in. The normal color cycling exos still have blocks like the marble that make them more special.
It could work. Probably need really fine-tuned balancing like you said. Too easy and existing players will cry foul that their hard earned ‘rare’ colour blocks have been made irrelevant, too hard and it’s wasted dev time as nobody bothers.
Alternate suggestion though. If the goal of this is to allow people to work towards a throw of the dice at colours they want, could a better solution not be to allow them to craft an expensive item that spawns an exo? Seems like it might be fairer in that everyone can access it, and more importantly it’s not restricted to those people who have access to a Sovereign.
Admittedly, there is a drawback here in that people will summon too many exos using this and cost Boundless too much in server costs, they could always put a limit on how many exos can be spawned like this at any one time, and how long they last for etc. It’d also give players themselves scope to do something about it when there hasn’t been an exo for a while.