This brings up the question of how Aragorn would disguise himself. Obviously, colored contacts are out, but grey eyes are not uncommon. Neither is dark hair, although I suppose Aragorn could have used some sort of organic dye to change his hair color. So what would Aragorn change about himself, besides his attire? He couldn't make himself taller or shorter, or give himself a humpback, because that would impede him in battle. So how would Aragorn change his features?
It is possible, even in this world, to change how people see your features (no, I am not smoking anything, but it's very hard to explain) especially if you have distinctive eyes. Aragorn's were "A pair of keen grey eyes." Perhaps this is what he did?
Also, do you think he would have made himself as bland as possible, or as distinctive as possible, so that if he returned to Rohan and Gondor, he would not match the definite image of Thorongil that people had?
Or perhaps Aragorn used some sort of elf-trick/strength of mind to disguise himself?
Or maybe... *pictures Aragorn in a trench coat and dark glasses*
