No, a colony only gives you control of the planet you put the colony on. The difference between a colony and an outpost is that an outpost only generates resources but can't do anything with them, while the colony will generate resources, but also gets population and once the pop is high enough, gets factories to build stuff with said resources. It's only in your starting system that you get control of every planet automatically, after that you can build a colony in another system but will still need to create outposts on all the other planets if you want them as well.