GR translation: coaltar-impossible orange-brown

[Mike Jing]

V693.8-19, P706.31-707.2   There were men called “army chaplains.” They
preached inside some of these buildings. There were actually soldiers, dead
now, who sat or stood, and listened. Holding on to what they could. Then
they went out, and some died before they got back inside a garrison-church
again. Clergymen, working for the army, stood up and talked to the men who
were going to die about God, death, nothingness, redemption, salvation.
It really happened. It was quite common.
       Even in a street used for that, still there will be one time, one
dyed afternoon (coaltar-impossible orange-brown, clear all the way
through), or one day of rain and clearing before bedtime, and in the yard
one hollyhock, circling in the wind, fresh with raindrops fat enough to be
chewed . . .

What does "coaltar-impossible" mean here?
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