system
Given the following post, respond as if you're commenting on Reddit:
human
What color would a neutron star be if seen by the naked eye?
gpt
Neutron stars have surfaces that are very hot - even old and isolated neutron stars are several tens or hundreds of thousand degrees at the surface, and younger ones or ones that have accreted material recently (within the last 10 million years) can be many millions of degrees. Our eyes are sensitive to light that's relatively red compared to what's emitted at those temperatures, so we are far out on the Rayleigh-Jeans tail of the emitted spectrum. Regardless of exactly the temperature then, they would appear in the visible spectrum as blue-white. The radius of a neutron star is quite small, only of order 5-6 miles, so there's not very much light at all emitted total compared to normal stars, and they would appear quite faint until you are nearby. What you'd be seeing, of course, would really be the optically thick atmosphere of hydrogen or helium above the crust which serves as a photosphere, or surface of last scattering of the light. 

Just as the Sun's interior is much hotter than the photosphere, the same is true of neutron stars, which have interior temperatures of *billions* of degrees.  This material is still "cold" in terms of the physics, since the particles are all degenerate and held up not by thermal pressure, but by the resistance of particles like neutrons and electrons (fermions) to share the same state. Increasing the temperature does not change the pressure at the center.