The answer to this question is the color black. Although every object can absorb and emit electromagnetic radiation, what determines the rate of heat transfer of such an object is its color. In other words, the rate of heat transfer of an object depends on its color.
This means if you have the same object in different colors, the object with black will absorb and radiate more electromagnetic radiation than others. The reason why black is the best radiator of electromagnetic energy is that it has the ability to absorb more radiation, causing an increase in the temperature of any object colored with black.
In the same vein, the more it absorbs electromagnetic energy, the more it radiates. This explains why those who are living in hot climates don't wear black clothing. It also explains why anything black is hotter than those with other colors.