黑色吸熱和釋放熱

Absorption and Radiation is two different process.
But u can remember "Easy come Easy go"
For black colour, Eneregy easy come(absorb) , also easy go (release energy)

Same for silvery object.

The absorption of thermal radiation (infrared) involves molecular vibrations. Molecules in a black body can respond to electromagentic waves of all wavelengths. They would absorpt all these waves and hence the body appears black.

When the body is heated to a temperature, the process is just reversed. Thermal vibration of molecules emits electromagnetic waves. Because these molecules vibrate in all possible frequencies, the waves emitted cover all possible frequencies

Following this concept, silvery white surface is a bad absorption of heat radiation, because molecules on the surface do not absorb the incoming thermal radiation. This thermal radiation is then reflected. The surface thus appears white.

When the temperature is raised, thermal vibrations of molecules would not leads to emission of electromagentic waves. Thus the surface of a silvery white object emits little thrmal radiation.