How much light a surface bounces back depends heavily on its colour. Black surfaces absorb nearly the entire visible spectrum, converting most of it into heat, which is why dark objects heat up fast in the sun. White surfaces do the opposite, scattering back almost all wavelengths of visible light in every direction. Even compared to a mirror, which reflects light sharply in one direction only, a white surface reflects a broader spread of incoming solar radiation overall. So white objects reflect the most solar radiation.