The blank color code on the warranty plate does not designate a white exterior, but a special exterior color of unknown designation. To determine the original paint color would require finding the car's build sheet or digging under the carpet, deep in the trunk, or under the dash pad to find an original spot of exterior paint. The DSO number of 721764 means this is the 1764th special order unit to come out of DSO 72 (San Jose, CA). No other historical information can be determined from the information provided or from the car's recent ebay auction.
I communicated with the seller during the auction that I believe the current color is close to Pace Car White, used exclusively on the 190 special Mustang Indianapolis 500 Pace Car coupes in April / May of 1964. The same paint code (color C, PPG code 8321) was used in Ford's truck line, where it was called Pure White. The car shows strong evidence of a very complete and thorough re-paint, so its original exterior color is still unknown.