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),

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.