Today I bring a simple how-to from a most mediocre painter...me. I tweeted this guy last week and got some positive feedback, so I figured I'd give away some of my trade secrets on how I did it...
Step 1: Paint your stealth suits in your chosen color scheme (in my case Codex Grey and Mechrite Red) and apply a generous black wash. This is the "shrouded" part.
Step 2: Decide how far along the field has been activated on each model and paint a jagged white line across the point where you want the shroud to end. Paint it uniformly across panels and gaps and make it look random. It's supposed to be an energy field spreading across, so make it look as such.
Step 3:
Now go back and paint the unshrouded part in your base colors again so they are brighter.
Step 4:
Finally, to make the white line look more like arcing energy, add a thinner line of blue inside the white. Again, make it jagged. And there you have it. Adding a little more fun to your stealthsuits.