If I make like Option #2, then I can make another option in the user cp options to override a user's default font and view the message in the forum's default style. Hope that makes sense.
But I'd like to point out, though it's probably obvious already, that this problem already exists if a user can set font colors in an individual post.
Or, if you are worried about that, then you might not want to install this hack in the first place.