Thanks Brian and Keith, for the clarification. Having said that, this page ( click on link here) on Richard Binder's site would have me think otherwise, so I guess you can see why some confusion arose. I know Richard has a disclaimer that the information should not be taken as "absolutely authoritative", but still there is big difference in the Copper and Brown barrel colours shown...
Esterbrook only ever advertised and marketed a copper colored pen. I've got quite a stack of Estie catalogs, ads, etc., and don't recall ever seeing an announcement for a brown esterbrook J. Some will call the darker copper, "Root Beer" but I don't go along with that designation. The pen is copper. Plain and simple. While you may find a difference in shading between various copper pens, there was only one color made. You'll find shade variations in the other colors as well, grey, green and blue particulalry, but I'm not going to give them special names to describe the colors like others have. Esterbrook surely received different stocks of plastic in which introduced the different shading. It was not intentional on their part.
These colour variations are a nice added feature of Esties. My Estie is definitely a "Copper"-coloured one, but it would be nice to find a "Blue" estie that is more purplish