Thanks for your reply.
Yes I have seen many mention it is ‘slops’ but then others say it has a particular colour code. Some also say the boot is the same as the firewall but my boot is an army green colour and has no resemblance to any other painted item. Hence my confusion.

All the black painted surfaces in the engine bay look the same at present but a good clean up may reveal differences. I might get some cutting compound and apply it to various items/areas and see how they compare with each other.