At high temperatures -- about 400 degrees and up -- a substantial part of the heat that reaches the food arrives in the form of infrared light waves rather than via hot air or steam.
The higher the temperature, the bigger the part that radiant heat plays in cooking. But this form of heat interacts with color in a profound way.
A silvery, mirror-like fish skin is even more reflective than a white car. About 90 percent of the radiant heat striking it simply bounces away. Because only around 10 percent of the energy sinks in and warms the fish, cooking initially creeps along slowly but steadily.
That changes rapidly, however, as soon as the food gets hot enough to brown. It's like changing from a white shirt to a black shirt on a sunny summer day.
As the food darkens, that 10 percent of energy absorbed rises by leaps and bounds, and the temperature at the surface of the food soars.
So learn your physics to understand how to be good in grilling! :)