If you’re going to be travelling somewhere dusty and/or polluted (such as China, SE Asia, India, etc) then choose grey t-shirts or something similar. Even in cold weather when you won’t sweat much – therefore not needing as frequent a change of clothes – the grime will show up something rotten on white shirts. Even black can look coated in dust of the right/wrong type. Grey’s good.
Credit where it’s due – Hans told me this.