when you say some of your wisteria is going white, I'll assume you mean the leaves, because it's not clear from your question. Second, I'll assume it's not some kind of mildew (a powdery deposit on the leaves), which leaves transition shock - if the wisteria was under shelter or inside when you bought it, and you just put it straight outside, it's the cold of the outside compared to where it was that's caused this. Should have been hardened off before planting, meaning stood outside during the day over ten days or so for extending periods, till eventually it was outside all night, to acclimatise the plant.