Darker colours are better absorbers of light and thereby become better radiators of heat. Black absorbs light in it's full spectrum.The colour of an object depends on the wavelengths of light reflected from the object.When a black object is illuminated by white light, all wavelengths are absorbed. That's why the object appears black.Light is a form of energy. When light is absorbed by a black object, the energy of the light is transferred to the object. The object will then emit the absorbed energy in the form of infrared heat. This conversion of light into heat is the basis for the first law of thermodynamics.In a nutshell, the darker the object, the higher the efficiency in heat emission because it is able to absorb the energy from all kinds of light.

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