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.
11th Parachute Brigade (France)
The 11th Parachute Brigade () is a unit of the French Army, dominantly infantry, part of the French Airborne Units and specialized in air combat and air assault. The Brigade's primary vocation is to project in emergency in order to contribute a first response to a situational crisis. An elite unit of the French Army, the brigade is commanded by a "général de brigade" (Brigadier General) with headquarters in Balma near Toulouse. The Brigade's soldiers and airborne Marines wear the red beret (amaranth) except for the Legionnaires of the 2nd Foreign Parachute Regiment who wear Green beret of the French Foreign Legion.