Reaper Master Series has a triad of D9highlighteep Ocean (shade) MArine Teal (mid-tone) and Surf Aqua (highlight).
I've got the first two and they are nice turquoises with a touch of green, you can sort of see them in action in this tutorial (NOT my work):
http://www.fingolfin.net/sophie.php
Vallejo's Model Colour Range also features a wonderful deep Turquoise simply named Turquoisewhich I used to do the robes on my Inquisitor. It' reminds me of tropical waters.
I hope that was at least a little helpful.