All bodies emit energy in the form of electro-magnetic radiation, (sometimes called electro-magnetic waves). The rate of emission of energy depends on the temperature of the body and the nature of its surface.

Similarly, all bodies absorb electro-magnetic radiation. The rate of absorption depends on the nature of the surface only.

The temperature of the darker tube increases more rapidly than the temperature of the shiny tube. When the source of energy is removed, the two tubes return to their initial temperature in about the same time.

On a sunny cloudless day try touching different coloured cars in a car park (beware of alarms!) Touch exposed "chromed" surfaces and compare their temperature with both light and dark coloured painted surfaces. The darker coloured surfaces are noticeably hotter.

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