White balance can be altered non-destructively during post-processing of a raw photo, so the white balance setting in camera is unimportant. The question is how to determine the correct white balance in post-processing. If you want to do better than simply adjusting each image to personal taste, a grey card is the answer. I carry around a small grey card in my pocket, then when the light changes, I waste a shot to capture the grey card (hand held and probably out of focus). In LR develop module, I adjust white balance for the card, then transfer (sync) that adjustment to nearby photos taken in similar light.