M9 White Balance
When I went to the Leica users workshop the advice was to shoot at a constant temperature and correct afterwards in Lightroom. That way a group of photos can be given a consistent correction ... and you live in the knowledge that there is no problem with the camera. Something else that is useful is to set the camera up so that you shoot RAW plus a low res B&W JPEG and with highlight clippings ON. That means you can quickly check for exposure (and probably save battery life since you won't be spending so long looking at the back of the camera); later you throw the JPGs away of course. Good luck....and watch out for dust on the sensor..it sucks it all up!