Which colour absorbs the most heat?

Black, because black is what we call a surface that reflects almost nothing - the light lands, is absorbed, and its energy becomes heat. White does the opposite, scattering most of it back, which is why houses in hot countries are whitewashed and why a black car left in the sun is unbearable.

The tidy rule has a famous exception. Bedouin robes are traditionally black, which by the obvious logic ought to be a terrible idea in a desert. A study in the 1980s put researchers in both colours and found no difference in the temperature that actually reached the skin: the black robe does get hotter, but the heat is carried away by the chimney of air moving inside the loose garment before it arrives.

The same principle scales up to the whole planet. Ice and snow reflect most of the sunlight landing on them; open ocean absorbs nearly all of it. So melting Arctic ice replaces a white surface with a dark one, which absorbs more, which melts more ice - one of the clearest feedback loops in the climate system, and it works for exactly the reason a black shirt is warmer.