Engine bay is yellow zinc chromate, yes a yellow-green color. The engine is multi-colored. Mostly different shades of natural metal with green, black , red, etc for hoses, wires, and electronic boxes.
Here is shot of an actual one. Looks like the bulkheads are dark gray, but I think they are just real dirty. You can see the yellow zinc chromate on the upper and lower access panels.
Hope that helps.
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