http://www.blackhat.co.uk/online_shop/product_info.php?cPath=21_39&products_id=62&osCsid=2efde75a31f4ad9c773da59bc7a00b25
I believe this is a metallic green. From the people who made one of the Citadel ranges of yesteryear.
With the new citadel range, its either mixing, or using green glazes.
Silver base colour, with a green glaze, and then highlights and glaze again perhaps.
Or gold base colour with blue glaze (not too strong a blue) to get the yellow metallic and blue glaze to create a green. - this would be a different effect to green over silver.
Spraying the glaze might be a good plan. Making your own might be a better plan.
Liquitex Glazing Medium is the ticket (although this dries glossy and would need a matt coat over the top) (kind of like citadel lahmian medium, only a much larger bottle)
Spraying the silver might be a good start too, army painter do a silver spray, allthough I can't comment if its a nice finish or not, as I've never tried it. I would spray whatever silver I like through my airbrush personally.