I made the trip to B&Q today for some sample pots and bought the 4 darkest, they don’t do neutral greys and looking at photos from 2015 it looks like the paint has faded substantially from the ultra dark navy blue back then.
I’m fairly sure the paint was Deep Space Echo:
But I also tested the other colours, and am wondering if the brownish one might work well with the arch:
Test patches and pots are in the same order left to right:
