The gun metal is shiny, and sort of silvery with lavender mixed in. I think that they tried for titanium, but missed it a little. It is attractive, but doesn't look like any gun metal I have ever seen.
The HA is dark green matte OD khaki.
I prefer the gun metal, but it is a matter of taste. The HA is supposedly more resistant to scratching, but I have been carrying my E2 GM for a few months in my pocket daily and it shows no signs of wear.
Hope this helps, Walt