The most widely used camouflage (also by regular infantry men) is the ERDL 4-color pattern. Developed in 1948 by the Engineers Research Development Laboratory and based on a German late-WWII pattern used by the Waffen-SS it was field-tested and approved by US Special Forces from early 1967 onwards, but was not available for distribution on a larger scale before 1969. The pattern was composed of yellow green (army shade 354), dark green (army shade 355), brown (army shade 356) and black (army shade 357)*. There are 2 variations of ERDL camo, known to collectors as 'green dominant' and 'brown dominant', referring to the dominant color in the pattern. The green dominant variant is the most often encountered, although the brown dominant version is not as rare as some people think. The USMC also used ERDL camouflage.
The South-Vietnamese ARVN (Army of the Republic of Vietnam) 'Tigerstripe'-pattern consisted of black stripes (with a white lining) on a green background, was very effective and immediate very popular by the US Special Forces, who used it when they could. Some regular infantrymen were able to get 'Tigerstripe' fatigues, but the main use of this pattern was reserved for SOG (Special Operations Group) and LRRP (Long Range Reconnaissance Patrol) troops. It was officially adopted by the US Military, and is still issued when needed.
The early 'Duck hunter' pattern was a direct development of the WWII-era camo pattern used mainly in the Pacific by both the Army and USMC. The base color was a light tan, to which green spots were added. the pattern was fased-out early in the conflict. There were multiple variants of this pattern in use. This type of camouflage was also known as 'Beo-gam', Vietnamese for Leopard.
*) according to Stanton's 'U.S. Army Uniforms of the Vietnam War' p.8
Right: example of ARVN 'Tiger stripe' pattern camo.
Courtesy of www.kamouflage.net
Image courtesy of Lee Emerson