All of the latest miniatures are all painted with contrast. I start with a zenithal highlight to strengthen their effect. Then I mix them out on the wet palette. When I said I mix some green in the grey, I used Creed Camo with Administratum Grey(?). I felt this created a nice field grey.
I do sometimes use washes to create additional filters, too, by spraying carriburg crimson f.ex., from left side-above, and then using catachan camo shade from right side underneath, to simulate different environmental influences. I've also used the lighter enchanted blue, to give the appearance of sci-fi ceiling lights. Like on the Space Hulk terminators.