You mean the carapace? Recalling from memory:
Base was Shadow Grey.
I then streaked on successive highlights that were watered down and applied them in gradually thinner patterns.
3:1 Shadow Grey/Wolf Grey
2:1 Shadow Grey/Wolf Grey
1:1 Shadow Grey/Wolf Grey
1:2 Shadow Grey/Wolf Grey
Wolf Grey
2:1 Wolf Grey/Ghost Grey
1:1 Wolf Grey/Ghost Grey
1:2 Wolf Grey/Ghost Grey
Ghost Grey
1:1 Ghost Grey/Dead White