Green beret
The 10th Special Forces Group (Airborne) had many OSS World War II veterans in their ranks when it was formed in 1952. They began to unofficially wear a berets of varying colour while training. The color green became favored because it was reminiscent of the World War II British Commando-type beret. The 10th Special Forces Group (Airborne) deployed to Bad Tolz, Germany in September 1953. The remaining cadre at Fort Bragg formed the 77th Special Forces Group. Members of the 77th SFG began searching through their collections of berets and settled on the Rifle Green colour of the British Rifle Regiments (as opposed to the Lovat Green of the Commandos) from Captain Mike de la Pena's collection. Captain Frank Dallas had the new beret designed and produced in small numbers for the members of the Special Forces.
Delta Force
The origin of the term operator in American special operations comes from the U.S. Army Special Forces (aka the Green Berets). The Army Special Forces was established in 1952, ten years before the Navy SEALs and 25 years before DELTA. Every other modern U.S. special operations unit in the Army, Navy, Air Force and Marines was established after 1977. In "Veritas: Journal of Army Special Operations History", Charles H. Briscoe states that the Army "Special Forces did not misappropriate the appellation. Unbeknownst to most members of the Army Special Operations Force (ARSOF) community, that moniker was adopted by the Special Forces in the mid-1950s." He goes on to state that all qualified enlisted and officers in Special Forces had to "voluntary subscribe to the provisions of the 'Code of the Special Forces Operator' and pledge themselves to its tenets by witnessed signature." This pre-dates every other special operations unit that currently uses the term/title operator.