The shape is quite similar to that of a bluebottle's, but the colour is completely different, when I say gold I mean gold as in wedding ring gold.
I've also noticed that they tend to walk a lot rather than fly (but yes they can still fly), and their reaction's aren't as quick as a bluebottle's as you can stand on them sometimes.
I know what you mean though ..in certain light they look greeny gold and gold in the sun.I think it's what is called a bottle fly as opposed to a bluebottle.
Sorry can't be of more help.!