Final answer:
Black T-shirts get warmer in the sun than white T-shirts because darker colors absorb more energy from electromagnetic waves.
Step-by-step explanation:
The reason a black T-shirt gets warmer in the sun than a white T-shirt is because darker colors absorb more energy from electromagnetic waves than lighter colors do.
Darker colors, like black, are better absorbers of radiation and therefore they absorb more heat from the sun's rays. This is why black objects, including black T-shirts, can become hotter when exposed to sunlight.