Could it have been that the artist just didn't know?
On the b/w still that he was painting over, would there have been any difference between silver and flesh (the rest of the cast) and so maybe he took it upon himself to humanize him.
Going back to my old Bond related stomping ground, for the Dr No lobby set, Connery's attire on the beach was blue trousers and blue top. The cards had the colours all over the place. A red and green combo being one such.
