I hope this helps.
The Stealth is triple-coated Cerakote - a flat, matte ceramic finish. It has a very, very slight textured feel; chalky perhaps? The button is solid black, not clear like the regular ProVari buttons. The top and end caps are matte black. The LED is blue and lights 50% lower then regular ProVaris (I'm not sure if this is true for the P3s). The finish will reflect direct light (as in the flash picture below), but not like the
satin shine of a Satin ProVari (look at the edges of the Silver Satin below). I don't have a Black Satin to compare it with for you - I PIF'd it. Forgive me, Willy.
The GMZ is Gun Metal colored ZenKote™ - ZenKote™ is a very hard, glossy finish Zen trademarked. It is a
process more than just a color coating. He explains it in detail to PB in an interview (I'll have to look for the link). When I asked Vape360 about it, he suggested I read about Physical Vapor Deposition (PVD):
Physical vapor deposition - Wikipedia, the free encyclopedia I read about half the page, then decided all I needed to know was that it was purple.
The ZenKote™ Provaris are high shine and have clear buttons. The finish feels slick, like polished stainless steel. Gun Metal is like a dark charcoal gray, but it reflects a blueish light. As an example of the reflection, my Princess Purple is very dark, like Welch's Grape Juice, but look how it shines and reflects the paper in natural light:
ETA: Here is the post that has the link to Zen's interview:
Official ProVari Radius Thread