Here is how I am painting my Necron scenery to make it look like catacombs on a Tomb World. I tried to make the process pretty quick and easy to apply to all of the different bits in the box.

Black Stone

1. First, I primed the scenery with Chaos Black , ensuring that I get good coverage. This will act as most of the basecoat too, so dont worry about going a little heavy.
2. Go over all of the scenery again with a thin coat of Abaddon Black . This is to make sure we have a consistent colour over all of the model.
3. Give all of the black portions a fairly heavy drybrush of Skavenblight Dinge .
4. Drybrush the black area again with a lighter pass of Stormvermin Fur .
5. Take some Stormvermin Fur and add a small amount of pure white (like Vallejo Dead White ) and add small selective highlights to points and corners. I wasnt too strict with ratios, bit I did mine about 4:1.
6. Mix Stormvermin Fur and white again, this time around 1:1 and add specular highlights to points and the centre of the last stages highlights.

Weathered Metal (Doors)

1. Drybrush Gunmetal Grey fairly heaving over the Abaddon Black basecoat from earlier, picking out all raised detail and adding texture to the flat surfaces.
2. Drybrush a little lighter with Duraluminum . I stuck to corners and edges where the above drybrush took really well, to add definition.
3. Now add final small highlights of a lighter metal like Chrome . I just pick out corners and very pronounced details.
4. I was tempted to call the doors done, but some parts of the doors looked a little too uniform, so I glazed certain panels with Seraphim Sepia to add some visual interest.

Metal Conduits/Additional Details

1. Basecoat with Leadbelcher .
2. Wash with Nuln Oil .
3. Drybrush lightly with Necron Compound .

Glowing Green Details

1. Basecoat with a pure white (I like Vallejo Dead White ).
2. Apply Warp Lightning over the white, either with an airbrush or in a thin layer.
3. Apply a small highlight with Vallejo Fluorescent Green . Again, this highlight can either be added with an airbrush or picked out with a detail brush.
4. If the above step called for a large highlight, feel free to bring it up to a pure white again, toward the point where the light would be emitted.