This and subsequent posts reflect my earlier comment about the exact nature of the original question not being clear.
a black body is a black body....its TEMPERATURE that matters.
Originally the question was about the nature of the main matter that is in neutron stars, that is pressurized neutrons. There was also one about how the star itself looks, but that one was answered with it being very hot and therefore glowing, I myself suspected that being from hot gas and plasma around the neutrons, but not the neutrons making the light.
The question on how pure neutrons, a pure wall of neutrons would affect light is yet unclear. I'm guessing studying that would be extremely hard, since it's not possible to replicate in a lab.