Realistic steel? There's nothing unrealistic about blackened or blued armor. In fact, polished steel would have been rare. Aside from expensive man-power to polish your armor, once you polish steel, and leave it blank, it rusts like crazy. Mind you, this is high carbon steel, not stainless. That means spending a lot of time maintaining armor every day. And if you're wearing armor, you're probaby at war, and you have better things to do with your time than sit around polishing your... armor.
Typical treatment would have been, if I'm not mistaken, via linseed oil or scale-blackening and resulted in a bluish or grey armor color. I believe painted armor was not unheard of as well.
how about a polish your armor mod then?

say, you can pay one of your soldiers to polish it for you and it will only last for a month before it starts to rust (so you can even add some rusty textures)
and to make it worth your while it can give you a slight bonus while its polished (say +1 to persuasion maybe because you look so good? and -1 when its rusty). and you can also have the soldier treat it with oil so to make it go back to its original state.
probably a lot more complicated then changing the textures though lol.. just an idea..
edit: btw does this work on the latest version?