I don’t know if this color is as much of a controversy on pre-xk as it is on xk, but here is what I found under the curved cover on the scuttle of my '38 SS.
The area within the four bolts seems to have had good protection from the elements for the past 81 years, as it is slightly lighter than the surrounding area.
I also got to wondering if those 4 extra small holes to the right of the cover could have been from an SS dealer’s badge? Were such badges popular among distributors, agents and dealers in the UK? Perhaps removed because it had the SS logo?