currently, the normal working dress for the British army is PCS (personal clothing system, or something like that), which is camo top and trousers in the MTP camp (Multi Terrain Pattern, google it to see examples). Originally this was the same uniform we wore on ops and exercise, but complaints about it* led to the (re-)introduction of the "barracks shirt" used for everyday use on camp (I say "re" because the barracks shirt is basically the previous Cs95 shirt design made in the new camo colours).
Previously to the adoption of camo as normal working dress (in the mid 90s with the CS95 woodland uniform), we only wore it for field use, and barracks dress was basically a civilian style collared shirt in beige, with a green tie and a green jumper over the top, and green "lightweight" trousers, with the stable belt (a wide decorative belt in branch of service colours) on top of the jumper.
as a side note, its worth pointing out that our issued "dress" uniform (no.2 dress) looks basically like the working dress uniform the army wore into the 1st world war.
obviously, we have coveralls and such for dirty jobs but the normal working dress we turn up to work in is the MTP camo uniform.
For the Imperial military, I would, personally, go with a simple, single colour set of uniform, with separate shirt and trousers, cut in a "smart" fashion (whatever that happens to be in 5000 AD). their might be significant local variation between domains and sectors as everyone "buys local" (take for example
this selection of authentic "feldgrau" ww2 german uniforms), and different sectors might have different rules of wearing of awards, specialist badges etc)
*while perfectly acceptable and practical for the field, it was felt to be a poor design for barracks use, being basically impossible to look smart in, and with Velcro pockets on the sleeves that were really useful in the field for carrying things, were ugly loud to use, and ruined the lines of the shirt, and the large chest pockets which doubled the material over the chest leaving the shirt too warm for comfort indoors. In short, it was good for use in the field, but too hot and ugly for everyday wear.