Kasrkins

Two Cadian Kasrkin models for Warhammer 40k. One of them is painted by me, the other by a friend. Posted because we have mild arguements over the paint scheme of my Kasrkins. Any opinions, excluding the minor details I missed until looking at the photo (Small patches of unpainted metal, for example)? And for that matter, any suggestions on how to keep frikking acryllic paints on metal media?

Kau
Carapace armor: Shadow Grey (Yes, it's a grey for some reason....) with Skull White spots
Fatigues: Codex Grey
Visor: Goblin Green
Hellgun: Chaos Black and Boltgun Metal.
Unit ID: Fiery Orange

Un-named Kasrkin
Carapace armor: Codex Grey
Fatigues: Fortress Grey
Visor: Enchanted Blue
Hellgun: Shadow Grey

And now to repaint the bastards....