Just the Red Hand sewed onto a garment, or a red cloth around one sleeve and the green breastplates in the later books.

Uniforms, per se, mostly seem to be reserved for elite royal units, like the Queen's Guard, who are going to be around the palace or court all the time. The Band is a multinational group, with recruits from five different nations by the time Mat is reunited with them in KoD, and the majority of descriptions are of their armor, and the differences in styles from each country. Historically, military uniforms actually derive from the livery worn by servants, because crossbowmen were not considered true warriors, and were instead classified as servants. When those started to be replaced by firearms, the custom of livery went with them, and eventually spread to the traditionally military arms, like cavalry. Nobles, meanwhile, would dress to demonstrate their familial allegiances. In WoT, that's who get most of the descriptions among the Band.

The places I would most expect a description of the Band's uniforms, if any, would be in either the chapter where they set off from Midean in LoC, or the one where they rejoin Mat in KoD.