The one on the end was actually sealed by someone who tried to convert it into a dwelling. There's a metal door frame installed in one of the doors!
As for the color, it could stand to be lightened up a bit by drybrushing some light tan on them. Considering the Cochran charcoal kilns haven't been used for many decades, I imagine the soot has eventually weathered away. I already dirtied my coke ovens up more than the original weathering, but maybe it's still too subtle.