Is it paint or alloy? All in my experience are black - but that is obviously an original box.
It could be paint, but I have a sneaking suspicion that it's alloy since the insides are also that colour. I'm assuming a previous owner swapped this in many years ago. None the less, I like it since it makes the engine look nicer among the other dirty bits.
I may try to paint the distributor cap cover the same colour some time. Speaking of which, I have a suspicion that the distributor cap cover is not original since it does not fit on properly. At least the cap and wires look pretty new when I took it off.