The collared shirt has two breast pockets and long sleeves with buttoned cuffs, and the front fastens with seven gray plastic buttons. Light-gray colored shirts remained uniform standard until 1955, when postal officials designated a new, light-blue color scheme.
As early as 1901, regulations permitted city delivery letter carriers to wear a shirt and tie without their jackets in hot weather.
National Association of Letter Carriers. “Dressed for Success: The Evolution of Letter Carrier Uniforms.” Postal Record. October 1986.
http://blue.usps.gov/postalhistory/histuniforms.htm (Accessed June 6, 2002)