Yeah, the red mage being the rapier wielding "duelist" archtype(who just happens to be capable of casting spells should the need arise) would fit well into a pirate theme. With that said, dont let anyone else stifle your creativity. Are you a black mage pirate who sailed the seas in search of new means of power? Are you a disgraced samurai who took to the seas to avoid the repercussions of your failure to your lord? Its your character, so do with it what you will.