It seem that during WWI Belgian made their khaki using a mix of "what they could find": perheaps PC10 + PC12, or a mix with French green...
Of course that would say that you can have a variety of +/- similar khakis...
That paint was fixed in the inter war, and our Foxes, Fireflies, SV5, Gladiators... were painted with a "standard" Belgian khaki.