Question

Why do certain colours absorb heat and certain colours reflect

Answer 1

it is depends upon the wavelength of different colours.
The more light the object absorbs, the more heat absorbed since light is energy. If you consider it a color, black absorbs the most heat. A black object absorbs all wavelengths of light and reflects none. Objects that are white, on the other hand,reflect all wavelengths of light and therefore absorb the least heat.