Light climbing out a gravity well loses energy. Unlike a object with mass, it doesn’t slow down as it loses energy, because it’s light - it can’t slow down. So it instead gets lower in frequency - “red-shifted”. Gamma rays become X-rays, which become ultraviolet light, which become blue visible light, which become red visible light, then infrared, microwave, and radio. Visible light climbing out of ordinary neutron star will be red shifted. Some of the red light will be invisible because it shifted into infrared.