Source - Army.mil
Black Beret. The tradition of wearing black berets began with armored units. In 1924 the British Royal Tank Regiment adopted the first modern military beret, based on the Scottish highland bonnet and French Bretonne beret. The regiment selected the headgear for its practicality—brimless for use with armored vehicle fire control sights and black to hide grease stains.
In the US Army, HQDA policy from 1973 through 1979 permitted local commanders to encourage morale-enhancing distinctions, and Armor and Armored Cavalry personnel wore black berets as distinctive headgear until CSA Bernard W. Rogers banned all such unofficial headgear in 1979. Rangers received authorization through AR 670-5, Uniform and Insignia, 30 January 1975, to wear black berets.
Previously, locally authorized black berets had been worn briefly by the 10th Ranger Company (Airborne), 45th Infantry Division, during the Korean War before their movement to Korea; Company F (LRP), 52d Infantry, 1st Infantry Division, in 1967 in the Republic of Vietnam; Company H (Ranger), 75th Infantry, 1st Cavalry Division, in 1970 in the Republic of Vietnam; and Company N (Ranger), 75th Infantry, 173d Airborne Brigade, in 1971 in the Republic of Vietnam.
Brown Beret. While HQDA’s morale-enhancing order was in force from 1973 to 1979, there was a proliferation of berets, in a rainbow of hues. In Alaska the 172d Infantry Brigade adopted an olive or brown beret. Members of the brigades 1/60th Infantry wore their brown beret with a light blue flash insignia. It was soon dropped when the Army standardized headgear policy in 1979 to limit beret wear to Special Forces, Airborne, and Ranger units.
That brown beret makes it look like you have a cow pie on your head.