How do you paint the bottom of your Raider/Ravager?

I am painting up my first Raider in the GW paint scheme. The body is Incubi Darkness but in looking at the pictures online and in the codex, I was unable to tell what color they used for the bottom plate of the vehicle (vehicle underside not passenger floor grid). Is it straight black with grey highlights or did they do Leadbelcher or something else entirely?

Any thoughts or suggestions?

Thanks

UM

Eyeballing the pics, it doesn't look black and it's definitely not leadbelcher. If I had to guess they've used a dark grey. Probably one of Eshin Grey/Skavenblight/Mechanicus, washed nuln oil and reapplied the grey neatly and lined the edges with a lighter version, probably Administratum Grey.