Sorry for necro-posting in a old "solved" question, but I think there is a better answer.
It is true, if your colony center falls in hostile territory of a native tribe for whatever reason (you may as well had build it there right away), you can not normally enter it by your own units.
It is also true, that eventually you may want to destroy (or federate, if you a High Native player) the tribe(s) responsible for this.
But if you do not want to do that (maybe just yet, maybe you even can't do it at the moment, maybe you want to federate it, but much later, maybe you enjoy the raids for some little leader experience, maybe you hope your churches and Missionary ability will finally convert it, whatever), there is still a work around to enter that colony:
1) move your unit so it stay on top of your colony center
2) open the "Unit List" from the top menu
3) clicking the unit on map selects it in the Unit List also
4) now go find your desired colony in the list (hint - if it new and empty, it probably will be down at the very end, if it your first, go for the top of the list)
5) collapse any sub-lists (by double-click on the containing name) you can so you get both your wanted unit and the colony name visible at once
6) drag and drop your unit name in the list over the colony name
7) congratulations, your unit is now inside the colony!
*) if you fail to do what I suggest in (5) you can also drag-scroll the list, by hovering the drag item over the top or bottom edge of the list box, but it may stuck sometimes... If that happen to you repeatedly, or you just too lazy, there another, less obvious way: make sure your unit is selected (red) in the list, scroll list to the colony name, and shift-select either the colony name itself, or any stuff already in the colony. Now drag-and-drop that to the colony name (yes, you actually can try and drop it on itself). You will get a message in info row, either "No circular containment" or "Item already contained under this" because of this, however, you will also succeed in your main task of placing what really wanted to get in. You should see the effect in the list, as well as unit disappearing from the map view.
*) pay attention if it say "Units not near each other" - in this case, make sure you really try to drop right thing in right place, if so, try to move your unit to the topmost or leftmost square of the colony center in question - one of those is the "true" location of that building for this purpose (but unit list drop-in should normally accept a unit from adjacent square as well in my experience).
Well, the Unit List is not the most user-friendly thing here is, and it certainly could have used some additional polish, but when you get a little used to it, what I say is much easier to do as it may sound at first. I successfully manage colonies in hostile territories this way (as well as swap units between leaders in the field and so forth).
Post edited April 23, 2015 by Enneagon
