Here's an example of what I'm doing that may work for this situation. Most of my rank and file are black suits with Forest green armor. My Sgts all have shock sticks and yellow stripes on the shoulder armor. My Female Caps have a lighter green and a pink plate on the chest, sgt had yellow stripes. My veteran caps, which are all just plastic figs, will have different colored armor, such as mars red, blue/white for snow.. with grey undersuits. I also have two painted dark blue with the "data visor" filed off to be my fleet troops, everyone knows they're always getting shot down.
I'll probably buy the roughnecks and I have the pathfinders (k9) on the way so no conversions there.
For the bugs, I have black with green stripes. I also have 5 with blue stripes which I use as proxies for figures that I don't have like the guard/assassin/burrower..
If anyone needs pictures, check out:
http://photos.yahoo.com/ph/nezeray/my_photos
Some of my figures like the Vets aren't up yet. Oh and look for the plasma bug on the display plaque. A mistake with lots of sand and glue turned into a cool mars landscape.
James / Nezeray