Ok.... it's been a while, but the car is now mine and I have it back home (well..... my home in Australia anyway).
I've looked most places on the car now.... even up by the wiper motor.... and the only colour I seem to be able to see is what looks like bordeaux red. I say looks like, as it seems darker than pictures I've seen of other cars this colour. At one point I almost thought it was chestnut brown.
There are a few spots which aren't this colour but they appear to be primer grey (some of the underside of the boot).
The car came off the German production line in Dec '51, before being delivered to Neue AMAG in Switzerland. So, unless anyone knows otherwise, from what I can make out it shouldn't be bordeaux red.