I think if you started using a different color, particularly one of the ones you mentioned, people would buy it if only because it's different from the standard grey. Grey is kind of boring, especially when it's the standard color that many other tarp manufacturers widely use. A custom grey/green would be pretty interesting to see, I think.
I have no aversion to gear with army connotations, unless it's actually army surplus gear, in which case I'd have to inspect the quality of the gear before buying it. However I think you've made enough of a name for Mountain Laurel Designs that you can use whatever color you want and you won't be in danger of anybody thinking it's army surplus gear.
My own preference for tarp color would be black. I don't know how to explain why, exactly. Black is just sexier than any other color.