I believe the term is "Bite me" Jan
I mean, right now I don't actually know how many tiles away you have to be before it becomes a colony. It would be useful to establish that knowledge, even if a settlers "Create City" button turned into a "Create Colony" button.
There should be two different options(Static and Dynamic), allowing the player to switch between the two via TXT. The advantage of Static is that you know where your Empires limits are. But to some, that can be a downside to the mod. What if you want to establish a country along the coast of a continent? Instead of making a circular empire, you make a Chile like one. The disadvantage with Static in this case is that if you stretch outside of that initial circle zone, you may found colonies when you don't want to.
Dynamic works as the picture describes: Your first city has a zone to build within. If you build a city within there, this new city(and ones after) emits a smaller zone. If you build out of a zone (in territory you want to get a foot in before someone else) you will establish a colony. But if you chain your cities, they can naturally expand to that point. In addition, only your zones matter; other civ city zones do not factor into you creating a colony or not.
Dynamic allows it so that you can slowly expand your empire naturally, without requiring magistrates outside of a certain zone. In this instance, actually far out cities from any of your other cities are Colonies, or placed on another continent. The downside to Dynamic is, depending on the game, you may never place colonies, unless you use the new Colonizer unit.
Both Static and Dynamic have their uses. Static is better for your usual game of Civilization, where you're going to have a core empire fighting for land from nearby civs. But in specialized instances, Dynamic is better, if say you play a game with less Civilizations, or you play on a geographical map.
In the end, it comes down to preference and taste. I say make both, let the players know there are two options (Leave static enabled by default), and let the players discover which way they prefer more, or at least leave extra gameplay options.
(I say all of this with the greatest respect for JFD's weekly schedule, and how little free time exists
)