Proceeding today with the base colours for my Imperial Knight (an interesting allied option for my Alpha Legion forces, I thought!), I wanted a colour scheme that would somehow resonate with them. Then I recalled that I had started a green colour scheme for my Warhound Titan. Everything clicked in to place and I decided that the Knight would be from the same Forge World as the Titan -- Perennia.
The undercoat here is black, airbrushed on. This was followed by two silvers (gunmetal and rune fang) airbrushed in to position. On top of this, I have applied three coats of (very) watered down zinc green from Vallejo airbrush range. The idea is to build up the colour in a layer of glaze, not unlike the shiny colours one often sees associated with Alpha Legion or Thousand Sons (or even a beast like a Scorpion of Khorne).
I'm pleased with the metallic green effect and will proceed on to the edging soon enough!