According to Ernest Hemingway (eye witness! It's him in the picture) in A Farewell to Arms, they were grey. In the case of the Fiat ambulances, I would expect them to be a greenish grey.
Thank you gentlemen, that's a great help, grey it is then.
Sorry it's taken so long for the reply I haven't been on here for a while... over a year it would appear!
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Has anyone else noticed "new and improved" seems to mean it doesn't work as well as it used to?