Kantor Blue is the primary armour colour of the Night Lords by Citadel; you can shade it with Nuln Oil or Drakenhof Nightshade, and make the lightning patterns with Lothern Blue and White Scar/Ulthuan Grey.
These videos go into it in more detail:
If you don't have Kantor Blue, I'm sure the other paint ranges you have will offer something that is similar enough