Grab the aircraft from here:

http://forums.x-plane.org/index.php?app=downloads&showfile=11474

and install by extracting the Twin Otter to somewhere in your x-plane/aircraft folder

Copy the 'Euroharmony Wild' folder to the twin otter/liveries/ path.

You can now select the livery from within x-planes Aircraft - Livery once the plane is loaded. If you would like to make it your default paint, open the aircraft in planemaker, select the Euroharmony livery and save the plane.

Happy Flying!