More on how the 737 was chosen from Lamar Muse's "Southwest Passage":

"Southwest's equipment had to be pure jet. [...] For our purposes, the options available to us were -- in order of general preference -- the Boeing 737-200, DC-9-30, BAC-111-400, DC-9-10, Boeing 737-100, and the French Caravelle. Rollin King and I spent a week surveying the operations of the California intrastate airline Pacific Southwest Airlines (PSA) at their headquarters in San Diego and confrimed that the Boeing 737 used by that airline was definitely our first preference.

[...] I learned that Boeing had some "white tail" 737s on hand built on speculation for PSA, Air California, and Piedmont Airlines, but all three had refused delivery of the aircraft due to the major depression then raging in the airline industry. Boeing had gone so far as to finish off the aircraft using those airlines' interior designs but had yet to paint the exteriors with any livery, thus the term "white-tail." However, they had some pretty fancy ideas about their value, and we got nowhere with Boeing on either price or financing terms.

Though there were plenty of the last four types on our list available, there were no used DC-9-30s -- our second preference -- on the market. We decided, however, that our best chance was with Douglas, which had expressed strong interest in meeting our requirements with new DC-9-30s, so Rollin and I in late March flew out to LAX, where a Douglas limousine picked us up to take us down to Long Beach to hammer out a deal with them. But the closer I got to Long Beach, the more I realized I really wanted Boeing 737-200s, and because few other airlines seemed interested in them, this seemed to be the moment to put maximum pressure on Boeing's sales department.

[...]

Upon arriving at the Douglas office complex, I went to a pay phone in the lobby and called Dan Palmer, Boeing's director of domestic sales. I told him where I was, what we were fixing to do, as well as what I would prefer to do. [...] I told him that Boeing had one hour to put us into their equipment -- otherwise forget it. Dan said he would be back to us within the hour, whichever way the decision went. He called back within thirty minutes. Boeing had accepted our proposal to the letter with an interest rate of 1.5 percent above prime. Our meeting with the Douglas people was barely underway, and it was a little embarrassing trying to explain to them what had happened, but they were gentlemen enough to give us a ride back to the airport. We caught the next flight back to Dallas, where we could now really get moving on tangible preparation for the commencement of scheduled service."

Drew,
In July 1971 (only a few weeks after SWA started), I flew on one of the 737s that was due to have gone originally to PSA, and I noticed the cabin interior had PSA's interior. (I had flown on PSA not long before that.) The sidewalls had drawings of a San Francisco Cable Car, the Theme Building at the L A Airport, and I think movie cameras.
Brian

The livery is kind of a reverse US Airways scheme?

Kind of reminds me of short-lived Fort Worth Air and their YS-11 turboprops that flew out of Meacham in the mid-80's.

Regarding the livery on the above Electra...

I smell a good idea for a special livery on one of LUV's 737's!