I prefer red wine over white when braising pork or beef, or if you want a lighter color, vermouth adds a nice herbiness over normal white wine. However, I'd second snowangel in that my first question would be if the meat was browned enough. Another fantastically flavorful way to braise pork shank, assuming the skin is still on, is to red-cook it in a chinese style: the braise with soy sauce, star anise, rock sugar, rice wine, and some ginger, at a minimum- though everyone has their own variation.