Uniform

A uniform is a type of clothing worn by members of an organization while participating in that organization's activity. Modern uniforms are most often worn by armed forces and paramilitary organizations such as police, emergency services, security guards, in some workplaces and schools and by inmates in prisons. In some countries, some other officials also wear uniforms in their duties; such is the case of the Commissioned Corps of the United States Public Health Service or the French prefects. For some public groups, such as police, it is illegal for non members to wear the uniform. Other uniforms are trade dresses (such as the brown uniforms of UPS).

Cobra
Cobra Officers, troops, and Vipers wear uniforms to indicate their unit. Named agents have more freedom to wear what they like.

G.I. Joe
As a Delta Force, G.I. Joe are not required to wear standard uniforms or adhere to dress and facial hair standards - indeed, since much of their work is covert, they are actually encouraged not to, as a group of buzz-headed jocks might stand out in, say, an Arabia bazaar.