These people are the workers on the High Frontier, they work the fields, keep the machinery going, construct the buildings, etc. Costume should be both practical and comfortable so usually some kind of utility trousers coupled with some kind of top, this can range from a shirt, body warmer, jacket, overcoat etc.
Insignia can vary, and can be where they are from, or previous postings/missions. New stuff on the High Frontier can be hard to come by in the civilian sector so there is a very prevalent “mend and make do” attitude.