O boy, let me dust off my memory:
- Skull White base coat
- Thraka Green wash on the entire model aswell
- Drybrush a mix of either Goblin Green or Scorpion Green ( can't really remember, but it would not make to much difference), together with Enchanted Blue, I'd say 6:1 ( as the blue is very dominant) until you have a Mostly greenish ghostly colour
- Use this mix, and add Skull White repeatedly to get the Highlights until some parts are ALMOST only Skull White.
- If you want some parts to be more dark, add some more Thraka Green Wash to it, to give it an extra shadow/depth-effect
That should do the trick basically
EDIT: The armour on the Ghosts is simple: Mithril Silver, with a was of ANY Speia colour ( I used Gryphonne Sepia). Highlight slightly with Mithril Silver again to your liking. Seriously guys, armour this way looks fantastic; old, corroded but still shiny at some spots ( at least that's what I think

)