As of 2015, illustrated images of shoulder patches worn in the U.S. Army are available on Army.mil and Wikipedia.com. In addition to pictures, both of these sites contain information on the different divisions of shoulder patch insignias worn by various formations of the military.
Shoulder patch insignias are considered part of a U.S. soldier's uniform. The patch corresponds with the headquarters where the soldier is stationed and is required to be worn at all times. These patches are usually designed with bright colors in order to be easily recognizable and are worn with the dress uniform. Soldiers are supplied with a second shoulder patch that is worn during combat. While its shape and design are the same, the colors have been muted so as to not draw attention from the enemy.