Yes, Holger, it must be the car #3537. The picture is matching (black tires) the trim too, (1M6E) but the outside color is 16 medium green. As you noted, the 3537 is not listed, except in the list of exported cars. It seems that the original owner was a Swiss guy, located in Nidau near Bienne.
There is some chance that I can add soon some more infos about the 3 cars Theo had: the green one in located near Bienne and the 2 other ones are also in Bienne. One will be restored, the other one (the white one) will be used as a spare parts source for the one which will be restored and then sold/scraped. Both owners promised me to give the details about these 3 cars.

Coming back to the anomaly: Ralph Messina wrote a message saying that it must be an anomaly. If I'm interpreting correctly the charts from the interiors, 1957 models trim code 1M6E should have a green back seat shell. This means that the lower part is right, but not the white upper part....