Corpsbadges in the American Civil War were originally worn by soldiers of the Union Army on the top of their army forage cap (kepi), left side of the hat, or over their left breast. The idea is attributed to Maj. Gen.Philip Kearny, who ordered the men in his division to sew a two-inch square of red cloth on their hats to avoid confusion on the battlefield. This idea was adopted by Maj. Gen. Joseph Hooker after he assumed command of the Army of the Potomac, so any soldier could be identified at a distance.
Co C 110th Pennsylvania Infantry after the Battle of Fredericksburg Va. An excellent photograph showing the Union Army white Diamond shaped III Corps Badges on the kepis
Maj. Gen. Daniel Butterfield, Hooker's chief of staff, was assigned the task of designing a distinctive shape for each corps badge. Butterfield also designated that each division in the corps should have a variation of the corps badge in a different color. Division badges were colored as follows:
Red — First division of corps
White — Second division of corps
Blue — Third division of corps
These were used in the United States' Army of the Potomac. For the most part, these rules were adopted by other Union Armies, however it was not universal. For example, the XIII Corps never adopted a badge, and the XIX Corps had the first division wear a red badge, the second division wear a blue badge, and the third division wear white.
For Army corps that had more than three divisions, the standardization was lost:
Yellow — Fourth division of XV Corps (reportedly Orange was also used for a 5th Division Badge)
Multicolor — Headquarters or artillery elements (certain corps)
The badges for enlisted men were cut from colored cloth, while officer's badges were privately made and of a higher quality. Metallic badges were often made by jewelers and were personalized for the user. The badges eventually became part of the Army regulations and a great source of regimental pride.