Visibility. The black star replaced the white star in the 1970's with the introduction of the Mobility Equipment Research and Development Center (MERDC) camouflage scheme. It was part of an overall effort to make vehicles less visible.

The original national symbol used by the army for vehicles was the same as the aircraft symbol: White star on blue circle, with a red dot in the middle, except Patton's 2nd Armored Division reversed the red and blue. In 1942, this was deemed too visible and replaced by a plain white star, except Armored Force vehicles, which used a yellow star, or yellow star with stripes (many M3 Lee tanks sported this scheme on the turret). Late in 1942 it was changed to just white stars. Some vehicles kept the white star on blue background on horizontal surfaces for easier air identification. It wasn't uncommon for soldiers to take mud or paint and mute the white colors, however (Mud was pretty widely used, as the olive drab color blended in poorly to North Africa's predominately brown terrain). During the North African campaign, it was thought the white star looked too much like the German Balkenkreuz, so a white or yellow ring was applied around the star, but this was dropped after the war.