ViewController.swift

 @IBAction func onChangeSelection(_ sender: Any) {
    let COLORS = ["ff0000","00ff00","0000ff"]
    let selection = selectionSegment.selectedSegmentIndex
    let color = COLORS[selection]
    let ref = Firestore.firestore().collection("settings").document("device1")
    ref.setData([
      "status": selection,
      "color": color
    ]){ err in
      if let err = err {
        print("Error writing document: \(err)")
      } else {
        print("Document successfully written!")
      }
    }
  }