As an editor, you need a pen that isn't black or blue to have contrast from the printed word. Red sends all kinds of "red flags" to people's brains because of all the lovely teachers we've had. (I've been paid to edit for 13 years, and I still react to red marks.) So, special colored pens are an editor's joy. My job has been especially emotional lately. Thus, colored pens to the rescue. It's really crazy how a "sunset orange," "fandago pink," "margarita green," or "hot aqua" pen can make all the difference.