As mentioned, non-reflective surfaces are good emitters as well as adsorbers. So the argument, AFAIUI, is that a surface which is non-reflective in the infrared

As mentioned, non-reflective surfaces are good emitters as well as adsorbers. So the argument, AFAIUI, is that a surface which is non-reflective in the infrared will radiate away more heat during the night. Crucially including heat that has been adsorbed in other wavelengths and then stored in the material during the day.