Stephen from ESV.org researched the "Origin of Red-Letter Bibles", i.e. Jesus' words printed in red. I too always wondered where they came about. I actually liked red-letter Bibles. Not because these parts are more God-breathed than the rest (though some think they are), but I just found it sometimes easier to search for a particular phrase, when you glance through a full page of text. Don't mind having keywords or connection words (because, therefore, for, in accordance to, etc) printed in different colours as well.