 To maintain secrecy, Loewy locked the papers and projects in his safe every day, putting his thumb's fingerprint on them.Finally, Mrs. Kennedy was consulted, choosing both the design proposal and its color, a blue-gray similar to that used in the interior of Air Force One.William Manchester, in his book "The Death of a President" (published by Michael Joseph in 1967) on page 246 gives another version of how the stamp was produced