I see several different discriptions of shades of green when it comes to chest rigs, puoches, slings, etc.

OD green, Ranger green, Foliage green, even one called Sewer green.

I'm not sure I really understand what color each of these are. Any explanations or better yet, visual comparison of these colors would be a big help.

What are your thoughts on the useful applications of these variations?

While we're at it, how about Khaki v. Coyote Tan v. Coyote Brown. What are the real differences?