Salt Weathered Green Armour

[Acez]

I've been spending considerable amounts of time making up some "classic" truescale Salamanders (in reference to Guilliman's style of doing truescale) and I want to give them a great paint job. Within the last year I've purchased an airbrush and that has helped make things go fast and better with consistent layers. But I want to try my hand at salt weathering the armour on not only the tanks, but also on the marines themselves. Where I'm stuck now though, is what colours would you use under the Warpstone Green (or it's equivalent). I normally see rust colours under, but was hoping to get some feedback from you guys as to what colours would be good to show underneath.

[Olis]

The only other viable colour than brown, imho, would be silver. Ceramite is supposedly silverish/grey naturally, iirc.