Came here with the same question, but there’s a good answer elsewhere in the thread that it’s about wavelengths: reflect where the sun is bright, and among those materials find one that is the most absorbent/emissive in the IR.

Absorption spectra and emission spectra are identical for thermodynamic reasons. But emissions happen in the infrared and absorption from sunlight happens at visible frequencies. So if you reflect visible light and absorb infrared light, you can stay cool in the Sun. Conversely, applying ultra-thin metal coatings to carbon-black objects can make them reflect infrared and absorb visible light, which is ideal for solar-thermal collectors.

The sun.

Black is both best radiator and best absorber. So it works perfectly in space (where you minimize incoming energy by turning it perpendicular to sun), and not so good on surface.

This material works by being reflective in spectrum, where most of sunlight energy is (which makes it white, as visible spectrum ~= sunlight on earth surface), and being 'black' (good radiator and absorber) in other spectra.