I'm sure I've seen a paint mix published somewhere, but can't find it at the moment. But it would have been for the dirty brown/olive drab colour found on the Western Front, which may have been very different to the theatre you wish to represent. Even then it would be inaccurate for the Western Front as shades would have differed depending on what was available to use. At the end of the day, paint your T what you feel happiest using and wait for the 'experts' to tell you it's wrong and then not be able to give you proof as to why.
Meanwhile, you may want to have a browse through here: http://1914-1918.invisionzone.com/forums/index.php?showtopic=72254&hl=