The color Khaki is perhaps one of the more over referenced and least understood colors. The word Khaki literally means "dust-colored" in Hindi and was the word given to British attempts to create a camoflauge by soaking white linen uniforms in tea. When dried, these uniforms had a faded brownish color that blended well with the dirty conditions of the dust in India at that time. However, over time, Khaki has been used to describe every color from basic tan, to coffee brown, to sandy brown, to brownish greens.
I know this doesn't answer your question directly, but it leads to my point of view. Basically, you can use your own imagination and come up with a color that could be considered Khaki Green and no one will argue with your choice.
If I were doing it, I'd take a light sandy brown and add just a very small touch of any generic green (military green, russian armor green, pine green, it really doesn't matter). If it looks green enough, you're done. If not, add a touch more until it looks good to you. If it looks too green, add some more sandy brown. As always, this is only my opinion and others will have their own ideas.
Enjoy your modeling...