SUCCESS!
The drybrushing didn't go as well as I'd hoped (it's already too light for it to really work), so I've had to manually highlight everything which means this is not going to be a quick project. 😅 But I'm really happy with how it's all come together. I really liked the hazard stripes above the doors on the top of my Into The Dark terrain as a really obvious way to highlight "HEY THERE'S A DOOR HERE, THE ENEMY MIGHT COME THROUGH IT" and I had been pondering how to do that here but without being yellow and black hazards stripes because that wouldn't really go. Turns out hazard stripes still work fine, you just need to theme them!
I'll need to tidy up the edges of the stripes and put a white highlight along the top wall edge, but these are going to look really sharp on the tabletop when I eventually get everything finished. I'm thinking I'll paint the Necrons themselves in a similar colour scheme as well.