Brunswick green is an old and beautiful color with a long history of use in England and Germany. The color was first manufactured from copper compounds in Braunschweig, Germany (a historical city in Lower Saxony which is known as Brunswick in English). Brunswick green is traditionally a very dark yellowish green which can look almost black. The color was first mass manufactured in the middle of the 18th century and it became an important color for machinery during the industrial revolution. Railroads in particular tended to use various shades of Brunswick green to paint their rolling stock. The color would start out black and then weather to a brighter green as the copper compounds oxidized.
England has deep and ancient ties to Old Saxony (the homeland of the Saxons, which includes the modern state of Lower Saxony), however the United Kingdom and Germany have sometimes fallen out rather badly (!). Thus in 1923 after the horrors of World War I, Brunswick green was renamed English Green (which just goes to show that “freedom fries” and suchlike political bowdlerization of names is hardly a uniquely American phenomena).