Take some shade of olive green and some shade of chocolate brown. Mix in any proportion that appeals. Add a very small touch of anything else that occurs to you.
Not being facetious - I think you would find an aeroplane somewhere on the British side of the lines that would be the exact shade that you've arrived at. If anybody tells you they have the definitive colour, ignore them. The real stuff was mixed to different degrees of tolerance and then subjected to harsh sun, stains and weather.
This is what appeals so much about PC10, it is the subtlest of hues, capable of infinite variety - a perfect foil in the display cabinet for the primary colours on the circus machines.
S