How uniform does a uniform need to be?

We were talking about Civil War uniforms today -- a digression in a discussion of the Geneva Conventions and the requirement that a lawful combatant wear a uniform. How uniform do uniforms need to be to be uniforms, I asked, realizing that I know very little about uniforms. I was surprised to read recently that in the Civil War, some Wisconsin soldiers had gray uniforms, because they ran out of blue cloth.

Well, did you know about the Zouave-style uniforms in the Civil War?



No! That astounded me. It seems so unmilitary to go for a fashion craze.