I leave monocular on auto. I also leave my scope on auto but feel I am in the minority. Most thermals have a count down to NUC option as it draws near. What I don't want to happen is forget to NUC and switch from monocular to gun and the screen is all messed up because it needs to NUC. Trying to NUC the scope with a coyote coming in hot to me is a bigger concern than the scope auto-NUCing as I shoot. As the thermal stays on, it will NUC less often as well. Find what you like, but I like Auto.
I personally, like black hot for finding a calling location as it is easier to see terrain features. I like white hot while scanning. Before having a thermal scope with colored reticles, I preferred shooting with black hot because the white reticle showed up better on black hot than black did on white hot. I have colored backgrounds and reticles now, and still shoot with black hot with a red reticle probably because that is what I am used to.
