It sounds like you're playing Dark Avatar, which has a tech tree branch for Extreme Colonization.

You can conquer a colony on a world that you could not colonize directly yourself, but to colonize a same-type world, you need the appropriate tech, e.g. Aquatic World Colonization.

The first level only gets you 50% production on a planet--to make them fully productive, you need the advanced level as well. These techs are more expensive in the latest DA updates, and at least on Gigantic maps, this means that there is a pretty long gap between the initial colony rush and the secondary rush for the extreme habitat worlds.

Ctrl-n creates a new map, with all new locations and resorces

whenever