Why do dark objects absorb more heat and light?

Heat and light are both forms of energy. Therefore, in terms of the object absorbing more heat and light what is really being observed is dark objects absorbing more energy. Light energy can be transferred into heat by exciting molecules in an object which has absorbed it, leading directly to increased heating in that object. This phenomenon is why dark objects will have get hotter than lighter ones. Different wavelengths of light contain different amounts of energy. Shorter wavelengths of light, such as violet, contain more energy than longer wavelengths of light, such as red. This means an object that absorbed violet wavelengths of light will absorb more energy than an object that absorbed red wavelengths of light, and thus have more energy to transfer into the form of heat. 

Lets take black objects for example. Black objects absorb all wavelengths of the color spectrum. White objects on the other hand, reflects all wavelengths of the color spectrum. Because dark objects absorb more wavelengths of light, they also absorb more energy. This energy from light causes molecules in the object to move more rapidly, generating heat. In the example of a white object, this does not happen because the object is reflecting all the wavelengths of light and the molecules inside the object are not being excited. Since no light energy is absorbed, no heat is generated. Hope this helps!