There are three army lists in the core Unity rules: Fringe-Spacers, Unity Agents and the K'Erin.
So where did these come from?
The Fringers are pretty much your average scavengers, scroungers, salvage crews, bandit gangs etc.
Fans of "rundown scifi" (Traveller, Firefly, Trigun etc.) tend to love these sorts and they can be modelled really well with gang models and a few adventurer types thrown in.
The army list permits the use of more rustic "nomads" as well as ex-army veterans so you can probably scrounge on your shelf and find a handful of suitable models.
Of course, being anarchic crazies, you can paint them any way you like.
A lot of table top gaming armies tend to look a bit same'ish, so being able to shake it up with purple hair, tattoos or bright red jackets will look very striking.
The Unity Agents take a little bit of inspiration from 40Ks inquisitors, but with a bit less grim-dark about them.
There's a few nice "special agent" models out there. but it can be a bit harder to fit into a game, especially as many generic games tend to aim for more of a military-sci-fi approach (unsurprising since we're wargaming after all).
The rest of the models in the unit will be various operatives and "volunteered" army guys, so most any human scifi troopers you have will work.
Standard color schemes in Unity is grey uniforms with dark red helmets or armor pieces, but since Agents have wide discretion, feel free to change that up.
What about the K'Erin then?
One of the enduring stereotypes in scifi is the "ritualistic warrior aliens".
Whether its Travellers Aslan, Klingons from Star Trek, Star Wars Wookies or the Turian in Mass Effect, these guys like to fight, typically have some sort of ritualized or highly structured existence and end up serving as mercenaries or forming very effective, expansionist armies.
Clash on the Fringe introduced the K'Erin as an example of the generic alien Warrior (originally introduced in No Stars In Sight) and with Unity Field Agent, it seemed reasonable to stop relegating them to being an example.
For K'Erin miniatures, there's a lot of options out there, so I tried to keep the description somewhat vague.
They're suggested as tending towards grey or even blue skin, as a nod to their Turian background, but go with anything you like.