Berets of the United States Army
U.S. Army Special Forces wear the green beret because of their link to the British Commandos of World War II. The first Ranger unit, commonly known as Darby's Rangers, was formed in Northern Ireland during the summer of 1942. On completion of training at the Commando Training Depot at Achnacarry Castle in Scotland, those Rangers had the right to wear the British Commando green beret, but it was not part of the regulation uniform at the time and was disallowed by the U.S. Army. 
The 10th Special Forces Group (Airborne) had many veterans of World War II and Korea in its ranks when it was formed in 1952. Members of the 10th SFG began to unofficially wear a variety of berets while training, some favoring the red or maroon airborne beret, the black beret, or the green commando beret. In 1953, a beret whose design was based on that of the Canadian Army pattern, and which was rifle-green in color, was chosen for wear by Special Forces units.
New Zealand Army
In recent years, a number of distinctive New Zealand features have appeared, while at the same time corps and regimental distinctions have been reduced in favor of standardised items of dress for reasons of supply rationalization and economy. Until 2002, berets were in various colours according to branch or unit. Since then, under a "one beret" policy, rifle-green has become the universal colour for this headdress, except for the tan beret of the New Zealand Special Air Service and the blue beret of the New Zealand Defence Force Military Police. On overseas service, a New Zealand flag badge and a white Kiwi on a circular black field with the words "New Zealand" are worn.