The Onion

Melanin is a response to ionizing ultraviolet light, which a lower-color-temperature sun would not have.

The funnier version of taking that hand-wave too seriously would be asking whether dark-skinned Kryptonians are more or less efficient at absorbing superpowers from Earth's yellow sun. It's the sort of goofy implication that arises from trying to justify the coincidences behind a just-so outcome.