Drewbles, I think you are being had!
Hang them out to dry. Have they offered any compensation, let them make the first offer and work from there. You have to be compensated for the additional 4 months of not having the car as ordered, or be prepared to accept black - but they have to pay for the mistake.
Ask where the green one was shipped - perhaps they sent the green one to a person waiting for the black one and it can be re-shipped at their cost. Make them do all the legwork.
I should clarify...
Car yard submitted order correctly (good thing)
Head Office for vehicle manufacturer in Australia submitted order to European plant incorrectly (bad thing)
Result: As far as head office was concerned, the correct vehicle was manufactured and shipped.
This is not the yards fault. They are so exceptionally apologetic. It looks like i'll manage to negotiate a loan car for the time it takes for my car to be re-made in the right colour, and shipped, and it'll be the equivalent model as well. I should also manage to beat them down more on price for the right one.
Either that, or they have to give me the black one for a stupidly good price, which they will not do (which is fine, I really do want my car in BRG).
Fun and games
