Personally, I would much prefer that the initial colony never shows up on a tile adjacent to any other. Why? Because the bonus it gives is no better than any basic improvement (+1 to adjacent whatever improvement type), and the initial colony itself gains no bonuses from being adjacent to anything else. There are much better things to have in tiles with lots of adjacency, especially if you're focusing the planet's production type. A factory next to another factory is a lot better than a factory next to an initial colony, as the production multiplier bonus from this is 0.1 rather than 0.05. The only time that the Initial Colony improvement is arguably better to have as the adjacent structure is when you're placing dissimilar improvements next to one another - say, a factory and a market which are both adjacent to the tile containing the Initial Colony, in which case you get a bonus of 0.05 to the manufacturing multiplier and a bonus of 0.05 to the wealth multiplier, whereas with, for example, a factory in the tile which would have been the initial colony you would get a 0.1 bonus to the manufacturing multiplier and no bonus to the wealth multiplier, or, as another example, if you had placed a Farm in that tile, you would end up with no bonuses to the multiplier. The only other time you're better off adjacent to an initial colony is in the very early stages of the colony's development, when you don't actually have much else that can give adjacency bonuses.
Initial colonies are not really all that great for tiles which are adjacent to other tiles. You're generally better off having the initial colony isolated off in a corner or something and placing structures that benefit from being next to each other in tiles which are adjacent to one another rather than having the initial colony take up an adjacency slot.
