This was a sudden inspiration. I did a sketch one day, and then I thought, as much as I want to leave this one to the reader, the image of the tuxedo and the rifle just stuck, and I went ahead and painted it. This is the primary protagonist, Alton Ely. A scanned pencil sketch painted with a Wacom tablet.
This is the concept sketch for the rifle Alton is holding in the fist image. It's a hybrid caseless assault rifle, using a conventional propellant to fire a saboted dart into magnetic rail acceleration, quite like the 'Chemrail' from Elysium. If you've seen that movie, the effects of such a rifle are very dramatically and realistically displayed. Basically, you don't want to get in front of this sort of thing. The hybrid design solves a whole host of the engineering hurdles that arise when you try to produce a manportable railgun. The biggest problem with today's chemical propellants is that the muzzle velocities reach a hard limit. Since magnetic acceleration is frictionless, it has the potential to increase those velocities by a huge margin. In this case, you fire a magnetic round with chemical propellant (but no brass casing, like the HK G11) into the second stage, which consists, essentially, of a pair of magnets which use a massive current to accelerate it to an even higher velocity.
It's all pretty macabre, but when you're writing novels sometimes you have to get that way.
This is my preliminary concept for Marianne/Janice's ship, Hotblack Desiato. The idea is incomplete in the drawing, but the principle is that what I've drawn isn't what you'd see. If you saw this ship against a lighter background, you'd only see the silhouette. Against space, it's just a cold black hole. As long as it's not pointing its engine at you, or emitting some sort of active signal (like radar or radio, or laser, or whatever), it's visually indistinguishable from the background. The surface would be completely featureless to the eye--it's just completely black. Thermodynamics does give us a hard time here, though, because even if we cool it and radiate heat away from the observer, it's still glowing in infrared, but there is a solution to this in the book which I won't ruin for you (because it's a key part of the plot).
Unfortunately for whoever flies this thing between worlds (it's not an interstellar ship, it's designed for maximum 1g Brachistochrone trajectories inside the solar system), it is necessary during the deceleration burn on a transfer to point the engine at the place you're headed to, making you visible to them for the length of the burn whether you like it or not. Fortunately there are countermeasures decoys for that if you're trying to make a tactical approach (though they're not going to fool anyone who can distinguish the energy output of your engines and the velocity of your craft from those of the decoys). You also have the advantage that wherever you're headed is a stationary target, and you are not.