I finally got my hands on a box of Nighthaunt from my local store.  I also picked up a bottle each of the new Citadel technical effects Hexwraith Flame and Nighthaunt Gloom. 
 
Incidentally I actually bought this set of 10 models to use in Frostgrave, not Age of Sigmar.  I wanted to have some undead for Frostgrave that were more on the supernatural ghostly side.  And I have to say, GW really did an amazing job with these models.  They are spectacular.
I started the models by doing a primer spray coat of Army Painter White.  Then I did a thin coat of Vallejo brush-on primer.
I applied the Citadel technical effects right over the white like you would with a wash.  I have to say that these new effects live up to their hype!  It works really well.  And it's indeed true as GW claimed.  You can do nothing but a white base coat and just wash over it with this stuff, and the models could be left just as is!
I was also pleased to discover that these are indeed a "one pass" wash very much like Secret Weapon Washes are.  They put down a very strong wash over white, you have to be careful not to put on too much.  In fact the blue one, Nighthaunt Gloom, is actually a bit too strong straight out of the bottle.  You could add a bit of water to it and it will still work very well.  The consistency of the technicals is very much like Secret Weapon's washes: a milk-like consistency with a pigment in the bottle that's more opaque than a standard wash.
Here you can see several different attempts at using the technicals. On one model I used both technicals just to see how a blue/green shade would look.  I also did some white drybrushing near the tips of all the ghostly shapes to try to do a transition look of ghostly to tangible. 
On the second set of five models I'm going to use both technical on the same model, where I use the blue on the cloak and upper half of the model, and then use the green on the lower parts of the ghostly shapes for a dual effect.
Here's the pics of what I've done so far!:
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