Background Trimming (Oval) Description
An oval-shaped embroidered item 1 3/8 inches (3.49cm) in height and  2 1/4 inches (5.72cm) in width overall, divided diagonally from upper right to lower left, blue over red (scarlet) edged with a 1/8 inch (.32cm) white border.

History
The background trimming was originally approved for the 173d Airborne Brigade on 13 April 2000.  It was redesignated for the 173d Airborne Brigade Combat Team on 12 January 2007. 

Source: The US Army Institute of Heraldry