Hi Paul . I thought by now you would have had a reply from a Flavia expert to your question!
All i can say is the engine bay of my Vignale is a sort of textured black finish, my 1800 coupe that i had before was the same, the boot lid is coloured as the rest of the car is, it may be how the under bonnet area
is mean't to be, but I don't know for sure, so now it's time for the experts to comment.
Regards Roger. P.S. how about some pics, and i presume not over heating now!