Thanks. I thought the colour was unexpected. I would imagine something more like this. I wonder if it is just the age.
No, it looks like patinated bronze which can be dark green or even black. When bronze oxidises it develops a stable patina which inhibits further oxidisation - that is why bronze tends to be preserved better in achaeological contexts, where iron just rusts away.
If the patina on the bronze was removed, it would stay a shiny 'bronze' colour for awhile, but then the new surface would oxidise again and you'd be back to having a dark patina.