Thank you all for your responses, as usual I got more confused than ever
Linen comes from hemp.. I guess I will ask some deadhead I know for a sample of dried pot leaves, and brush it with varnish , take a picture, turn it to greyscale and match it with wartime photos!
Just kidding.. I don't know what exactly does Dan San mean with "beige" and how that relates to commonly available pigments but it seems it would be a base of buff slightly brownish that turns yellowish when doped.
Certainly we can rule out dark yellow and the greenish yellow used in the Osprey profiles *yuck*
Summing it up, it seems to be the color of cafe au lait, with more milk than coffee