Actually, I decided that a generic Imperial Officer torso would come in handy, so I made one based on the official minifig. During the process, I noticed that Tarkin has a better belt and wears his rank pips in a different location, with two code cylinders, where the normal officer has one, so I gave them all the better belt and made a blank torso and pips/cylinders that can be added on to make custom configurations.
For a guide to the common ranks insignia configurations used in the empire, consult this wookiepedia page. Expect a headache though, as the costumers made no effort at all to follow any form of logic or common sense, so a lot of it has had to be retrofitted to make it work. Still, there are some basic standards from captains through Grand Moffs, and that page will help you if you want to make someone specific.
What does all of this have to do with Thrawn? Not so much. Being the student of art that he was, he kept a very simple uniform design with fewer lines, no cylinders and a different belt. Still, it was an easy change to make.
End result? A pile of torsos that could make anyone from a lowly pilot all the way to Tarkin and Thrawn.
600dpi as always, colours drawn in such a way that you can simply select and fill to replace any of them with something else. Need a purple officer? You can do it easily (and I'd expect to see a pic of that :-D)
Tarkin, dark grey and white
Standard officer, dark grey, black, white
One and two cylinder variations without rank. Use the addons to choose rank, or modify the Thrawn torso to include a cylinder.
Enjoy, and please feel free to comment!