Background Trimming (Oval) Description
An oval-shaped embroidered device edged with a 1/8 inch (.32cm) yellow border, the overall dimensions 1 3/8 inches (3.49cm) in height and 2 1/4 inches (5.72cm) in width, divided equally into three stripes, gray, white and black, and bearing three yellow lightning flashes, upper left to lower right.

History
The background trimming was approved on 8 Dec 1986.

Source: The US Army Institute of Heraldry