It is a known fact that all objects gives off energy. At the same time, all objects takes in energy, too. The color of an object affects what colors of light the object gives off and what it absorbs (National Energy Technology Laboratory, 2001).
The color of an object relies on the wavelengths of colors reflected from the object. A red apple has a red color because the red wavelengths in white light are reflected and other wavelengths are absorbed. But if a red apple were to be illuminated by light that had no red wavelengths, the apple would appear almost black.
The reason material looks dark is it absorbs most of the light that hits it. On the other hand, a material that cannot absorb radiation will reflect it to your eyes, making the material look like the color of the light and giving it a lighter hue. It naturally follows then that if a surface absorbs most of the light hitting it, the surface heats up quickly.
Black or dark colored materials and objects give off and absorb in heat the fastest. The reason for this is that lighter colors have a greater Albedo, which means, they reflect more light. Instead of thinking of dark colors as absorbers of heat, darker colors are actually better absorbers of light. Darker colors absorb comparatively more light. Since light is energy, an absorption would increase a materials temperature. Hence, darker colors become better radiators of heat.
It is important to note that an object appears white if it reflects all colors and black if it absorbs all colors. Naturally there are different degrees of color and therefore degrees of absorption. So, too, the type of material will affect its relative heating. An object with a dull black (non-reflective) finish will absorb the most energy and reflect the least (National Energy Technology Laboratory, 2001).
When a black object is illuminated by white light, all wavelengths are absorbed and none are reflected. As a result, the object appears black when we look at it. When light is absorbed by a black object, the energy carried by the light doesn’t just disappear. It raises the energy of the object that absorbs the light. The object, in turn, releases the absorbed energy from light by emitting longer wavelength, lower energy infrared (heat).
This transformation of light into heat is the key to understanding the whole process because it accounts for the law of conservation of energy. Light just doesn’t disappear when it strikes a black object. It is transformed into another kind of radiation that is either radiated from or retained within the black object. The darker the object, the better its emission of heat because it absorbs light better.
The bottom line is the reason dark colors are dark is that they absorb light instead of reflecting it. Since light is energy, absorbing light makes dark color hotter.