As early as 1945, long before the Air Force became an independent service, its leaders were looking at the possibility of obtaining a distinctive new uniform. By 1946 it was clear that it would be some shade of blue. In January 1948, President Truman approved a new uniform for the Air Force, but Congress would not approve the funding. In January 1949, the Air Force and Army addressed the issue again. This time there would be no extra costs. The blue cloth would be introduced as a normal replacement procurement in 1950.
On 18 January 1949, President Truman again approved a distinctive blue uniform for the Air force. A week later (25 January) the Air Force Chief of Staff, General Hoyt Vandenberg, spread the word that the blue uniform had been approved and would be available for distribution by 1 September 1950. He clearly stated that no one should purchase a blue uniform until "full instructions, specifications, and samples of cloth" were available.
On 8 April 1949, Air Force Letter 35-46 stated that the new Air Force blue winter uniform (shade #84) for men was available for purchase and immediate use. Distribution of blue uniforms would be made when stocks were available and general issue to airmen was expected to occur by 1 September 1950.
Read this unpublished study: The Air Force Uniform: a Brief History, by Sheldon A. Goldberg, Center for Air Force History, August 1992.
See the National Museum of the Air Force section on the uniform changeover.
See the Air Force Enlisted Heritage Research Institute for pictures of Air Force uniforms through the years.
See this unofficial collector's site for examples of early USAF #84 blue uniforms.