Good choice on craftworld, Im just finishing my own ulthwe army. As to your question I used the
GW bone colour scheme as outlined by Duncan below.
https://www.youtube.com/watch?v=asu5OuAckIE
For the black you have a few options. I used Sotek Green and Temple Guard Blue to edge highlight the armour which gives a really futuristic, "Matrix" esque flow to the black, however you could use
GWs other "clean" or "matte" blacks which incorporate more greys and subtle blues.
If you want an eye candy take on pro ulthwe stylings check out Darren Lathams instagram below, he uses more of a clean black style, however if you want to go all out sci fi, then perhaps the temple guard blue might be for you
https://www.instagram.com/p/BpwLZtdH3i4/