Depends on the year and what it came in.
There's dark green-blue, probably two other greens (one quite light), dark red, dark blue, "tangerine", and bronze.
A '40 sedan delivery stock engine would most likely be "dark green", which was usually a bluish-grayish-green. The color would change over time, with heat, and a newly rebuilt engine could be a totally different color.
https://myflatheadford.com/little-help-engine-color-us/