IMTU, the Solar Triumvirate uniforms are pretty traditional. Ofcourse, duty uniforms are functional enough for the 2400's battlefield: Infantry troops wear their Arachsynth Combat Environment Suits and full helmets (with vision, hearing and comm aids installed and a microcomp displaying info and maps on the visor, ofcourse). For Marines who train in Combat Armor, this is also their Dress Uniform.
However, the dress uniforms of most units follow the centuries-old buttoned style, drawing on both the British/Israeli, Japanese and Russian styles. Tradition is a strong force in the Triumvirate; most units have an old-terra "origin", even if this "origin" was 400 years old (and almost 200 of them are the total chaos of the Stagnation).
In the Serpentis Quadrant Alliance, on the other hand, the Triumvirate traditions are usually viewed as anathema; Pomp and ritual are scorned as pointless, reactionary trappings. The Alliance uniforms are simple and utalitarian, usually consisting of long, multi-pocketed high-durability BDU pants, colored in a camoflage pattern (which could be changed by a simple integral controller to whatever camoflage pattern appropriate), and a T-shirt, usually black or red colored (unless you change it to camo, which is easy - TL8+ cloth could change pattern with the touch of a button), with the unit's insignia printed in front and the Alliance symbol printed behind. Duty uniform adds a multi-pocketed vest over the T-shirt; longer, cold-weather clothes are also available. Each crew member wears either a bandana, a scarf, a shawl or a head kerchief - whichever they choose, all are pretty fashionable in the Alliance - usually showing the unit's unofficial logo.
Alliance ranks are shoulder-mounted plates (think Israeli or Russian style) and are worn on shoulder-straps (is this the term?) on the soldier's vest.
All Alliance services use similar uniforms (with different symbols/logos), with the Marines being the most strict about dress code and the Scouts usually wearing whatever is comfortable and suitable for their mission unless they are on parade.
Both navies (and the Consortium navy as well) use color to designate their Vacc-suits.