how hard is it to recolor/alter clothing?

[kamenkewl]

i'm really new to using mods, let alone making them. (i've only ever retextured things in the old sims games) so i was just wondering, how much of a process would it be to make a new clothing item, or to add something to an existing one? basically, i'm looking for an item that'd be a plain green army jacket, similar to the army/millitary fatigues, but worn open instead of buttoned/zippered up. i'm guessing something like that would require to be modelled from scratch? again, i have no experience here so i'm more just curious ^^;