Hah, finally found the nerve to post here...
So a while back I've been doing some contextual research for a historical/literary/cultural assignment on Mesopotamia. It's kind of difficult to fully study everything about this civilization, but I did manage to find some small sections in a few articles dealing with Sumerian warfare, specifically the standard weapons and armor used, etcetera.
I don't know if such things can be properly called uniforms, since their function is of a practical nature, and I don't really know if the Sumerians intended for their weapons and armor to bear particular identification. Although, this being warfare, then it must be practical to do so. I don't know.
But here are some articles I found on the subject. What do you think? Is it safe to call them the earliest uniforms in human history? 'Cause the Sumerians certainly have the earliest copper helmet discovered.