Averland gets done a lot (I have a averland army), so i would suggest going for a Province that doesnt get done as much. Ostland can be very striking with black, off white, and red. I dont know if I have ever seen a Wissenland army with red, grey, black and a little yellow. Talabheim gets done a lot as well but not Talabecland. Ostermark is another province that I dont think I have ever seen, they have off white, magenta/red, black and a little yellow. It seems like the armies that get a lot of attention are, Averland, Middenland/Middenheim, Talabheim, and Reikland/Altdorf. As long as you stay away from those you should have a very unique army.
Another option is to have mercenaries from adjacent provinces. This is something else I did to break up my army. I have a unit of handgunners, and a mortor from Nuln and a unit of archers from stirland. You could go for the skittles empire army and have each unit be from a different province or city but those armies look very busy.
I find character can be added to an army by painting the knights as an order instead of the same theme as the army. You could go either for a fluff theme or a similar paint scheme. For example, my Averland army is supported by a large group of Knights of the blazing sun, which fits both categories.