I'll be digging into my engine/trans/overdrive soon and may find more traces of paint on rusty parts or under the dirt/grease crust. Gray is my engine color & seems to be on other engine block parts I have except for the cylinder head from Brazil which is a nice green color.
I found this post from quite a while back by Aeroman that's very similar to the Darrin post but not as extensive, and wonder if the Darrin & Aero power trains were painted the same in their respective colors:
Peripherals: Black for valve cover, starter, generator, air cleaner.
Natural metal: distributor, carburetor, exhaust manifold.
Engine color: timing cover, oil pan, bell housing, crankshaft pulley, harmonic balancer.
I can add that my throttle linkage is black.
Speaking of black, some of what I've found under hood is gloss and some semi/satin.