Chris i have try the Khaki for the merkave ( i havent built yet though) due to color compatible its is not easy. I only try testor amour sand on my Ti 67 isreali t 55 capture.
However i did ask around someone told me that u can undercaot the merkavwe with lighter shade of green and cover it with lighted yellow sand of tamiya, that means mix sand color with white .
the other way maybe use khaki mix with white and light green.
any try this website http://idfmodelling.free.fr/articles.html, it did mentioned something on the color
however i havent done my model yet im waiting for eduard parts to arrvie for my merkava III