The Taranko colony was a Federation colony.

In 2370, the colony was in need of medical supplies. The USS Enterprise-D took up the needed supplies from the USS Lexington and delivered them to the Taranko colony. (TNG: "Thine Own Self")

This colony was only mentioned in dialogue.
According to Star Trek: Star Charts ("United Federation of Planets I"), by 2378, Taranko colony had become a Federation member.