Engine color-was oil pan painted?

[od-gmc]

I have two trucks that were built about 2 months apart (11/43 and 1/44). The earlier truck is a European return and engine was rebuilt by the French. The other I believe never left the US. Both show the engine to be green. The earlier is the darker kelly green that most people are showing but the second is more of a teal green. I will post a pic of each if I can get a good picture. My main question is that on both engines it appears that the oil pan, both upper and lower, do not seem to be painted. The European return truck was very well taken care of even after the return to the US and the pan looks to have been coated with some type of corrosion prevention (galvinized, cad plating, etc). It is not rusted, just dull metal. The second engine does show rust on the pan but the truck has spent a hard life and set unused for many years. Has anyone else seen this? Thanks.