This Legion is arguably the most difficult to categorically say what colour they use for their armour.
Historically they were like this.
I have seen many paint schemes in between these as well and they all look good, well maybe not the purple and green one.
Now the latest version from Forge World looks like this.
I scoured many forums and blogs looking for the recipe and I came across this paint.
The first thing I noticed is it has a warning on the side so read that first.
Some other observations, it is really thick but apparently can be diluted to use with an air brush. To this end I diluted my paint with a drying retarder which caused it to trap air bubbles within the paint so be wary of that. I also had to apply several layers to get the blue I wanted, this can lead to obscuring detail. Applying a wash for shading can be tricky as the dried paint surface does not 'hold' the shade very well.
Here are my test results on a spare terminator model.
I started with a metal base colour
Then applied the Tamiya x23
Not as light as the Forge World stuff but pretty good.
Now that I am happy with the outcome I can start on my Betrayal of Calth Miniatures.