After the lighter patches, I applied an all-over wash of Humbrol 140 Gull Grey (the genuine article, from a 1980s tin that had never been opened) followed by drybrushing the whole model with Rackham Sharp Grey (another paint you can’t get anymore, as the company went under about fifteen years ago):
Unfortunately, the contrast between base, wash, and drybrush colours is too small. You can see I applied them if you compare the wheels that have just XF-81 on them to the ones with the full treatment below:
… but that’s about it 
It’s not really more apparent IRL than in these photos, so I need to do it again with colours that are a bit darker and lighter.