I'm not entirely clear on whether you are asking about the specific A7V named "Wotan", or about A7V tanks in general. Thus:
- According to The German A7V Tank and the Captured British Mark IV Tanks of World War I (Hundleby & Strasheim, 1990), the A7V tanks could be seen with and without camouflage at various times. Uncamouflaged ones were painted overall field grey, while the more common types of camouflage probably used patches of pale green, red-brown and/or yellow-brown over the field grey base. The camouflaged tanks all had individual patterns, but if you want to simply build a generic vehicle, applying large patches of two of the camouflage colors will probably do.
- The same book says A7V no. 563, Wotan, was not camouflaged. It was plain field grey with two iron crosses and a Roman number III on both sides, plus crosses and name on front and rear. It later had no markings at all.