Here's two WIP shots of the Riptide that I am doing that may spawn a Tau army.
Plain basecoat of Minitaire Nautilus Blue. It turned out to be more greeny blue than I expected, bit I went with it.
I went through 2 stages of airbrush high lighting. The first colour was Minitaire Spellsinger Blue, and the second was a warmer grey - Minitaire Desolate Earth.