Some AS-90's also come in all over British green so if you dont want to mask you can either chose that or tan.The green varies quiet alot in tone and I always use a mix of Tamiya Nato green and olive drab,it's not quiet the same as the bronze green that has been mentioned.
As for the real life tan well that varies from tan to stone so you can use a mix of desert yellow/buff to desert yellow/dark yellow depending on how early or late you want to depict the vehicle and you wont be far wrong.