^ Unless the Federation considers all colonies within its borders to be "Federation colonies."
Why would they? That would be the mentality of some ruthless conquering power that believed it ruled over all others by default, but that's not the way the Federation thinks.
I think we should clarify the terms here before proceeding. A colony, formally, is a physically separate territory or settlement that remains politically subject to or connected with its parent state. That means a colony founded by United Earth before the Federation was founded would be a United Earth colony. However, since that colony would be a political extension of UE, it would thus presumably have become a Federation colony when UE became a Federation member.
However -- the key that makes something a colony is that it remains politically linked to and governed by the state.
The folks in "The Masterpiece Society" called their settlement the Genome colony, but they must have been using a more informal definition of the word, like the way it's used when talking about an artists' colony -- an enclave or community of people with shared interests, origins, or occupations. Politically speaking, Moab IV/Genome was not a colony at all, but an independent nation. It wasn't governed by Earth or the Federation; nobody even knew it was there. The Federation would've had no more right to lay claim to it, or any other politically independent human population, than they would've had to annex Bajor or Ferenginar.