The lightest blue I used was actually ice blue but that doesn't exist anymore with citadel so I think athermatic blue fills that roll but not sure.

1. Base Incubi Darkness
2. Layer Altdorf Guard Blue wet blend
3. Layer Calgar Blue wet blend
4. Clean up Incubi Darkness
5. Wash Drakenhof Nightshade
6. Layer Calgar Blue light wet blend then edge highlight and stipple around the blend
7. Layer Aethermatic Blue edge highlight and stipple
8. Highlight :ulthuan grey edge highlight and stipple