Can anytbody help me in providing a chart/list of different dirt colours of the different theaters both when dried and wet. I.e Russian, western Europe, southern Europe, africa etc.

That´s a difficult question.
I´d say there is no one or two colours that are "right" for each soil type. Natural soil is always a mixture of many elements and the color is never consistent even within a small area.
To make realistic soil I doubt there is any other way than enough reference material, either real photos or pics of another dioramas that has the look you´re looking for. Anywhere you go the soil type is very different, let alone a whole war theater...

I´d suggest going on with searching for some how-to articles about making groundwork to get some basic ideas of the different techniques and then use the ones that suit your purpose.

If you had a pic on you or some idea of a particular scene in particular place, it would be easier to help out and suggest colours and techniques!

Toni

PS. I´m making some very basic Finnish forest groundwork at the moment, and so far it contains five different soil types (layers), according to the real thing...I have all the reference next to my front door and it still ain´t easy!

hi there! for me the best way to make a realistic soil is to use the real thing...soil. in my last diorama, i used real garden soil which is fine in texture if you like you can visit this site where i explained the way i make my groundwork. hope it helps

http://users.skynet.be/automotomover/main.htm

my works are the three rally cars. i explained the process in the subaru diorama