Delta Air Lines' SkyTeam special for the PMDG Boeing 737-700, based on the real livery which is currently on a 737-800 in real life.
To install, unzip N3758Y.zip, then open PMDG Operations Center, select 'Livery utilities' from the 'Aircraft and Liveries' menu, click 'Install from PTP' in the lower left, select N3758Y.ptp in the folder you downloaded it to, and enjoy!