> During a polar night it gets so dark that once you’re out of flashlight range it doesn’t matter.
During the polar night the moon is up 1/2 the time, and it's from 1/2 full to full to 1/2 full, so there is still a source of light at least 1/2 the time.
Making them black to save on heating is a good point though. Same with wind blown snow being the main issue with visibility.
Black would also radiate more energy out though. And there's a lot more energyv that can go out than in, in winter. I would imagine using silver colored would be best for insulation.
Why not make them day glow yellow or something, so they are always visible?