Red light (R) has the lowest frequency of the visible spectrum. Blue Light (B) has the highest frequency. White light is the combination of all the frequencies of light. The color something reflects is the color you see. So, if you wear a black shirt on a hot day, you'd absorb all the frequencies of light (every color). According to the first law of thermodynamics, energy can neither be created nor destroyed. So when light hits an object, the energy has to go somewhere. Energy can change forms. So the light energy changes into heat energy, heating the air molecules in the Earth's atmosphere and heating the surface of whatever the color is on, like your shirt. How hot the colored surface gets depends on what color it is because that describes what frequency(s) light it absorbs.