The image below is of a pork butt, that I started at 250F, then realized I was not going to make it. I changed the heat, brought it up to 350F and let it ride. As you can see, that bark is quite dark with some areas that appear charred. Although not perfect, there was no bitterness I could detect. Nobody complained. I did pan and foil for the last hour or so, this softened the bark up a bit, as did the 30 minute rest as i drove to my destination.
