I used to work for a subsidiary of Sherwin Williams as a paint shader and dug thru their older files and found that in the Dimension line of automotive paints, Olive Green Mica is a near perfect match. I had them add a small amount of black to the mix to bring the color down slightly as the standard mix seemed a bit too bright to me. The end result matches the paint that one of our club members used to supply in pint cans for the 51-53, Henry J and Darrin engines.
And yes, the paint that Phil Hirsch claims is correct for the Darrin is not. His paint is a match to the 49-50 Kaisers and Frazers using the 2 bbl carburetor equipped engines.