You are correct to tell blond and brun only qualify the hair color when we say il est blond or elle est brune. Brun and blond are both commonly used as adjectives as well as substantives.

There is no term I’m aware of for a combination of dark hair and light skin.

What could be used is: un brun / une brune à la peau claire.

In addition to bronzé (sun tanned), there is a word that includes naturally dark skins, basané, but beware they might carry a pejorative connotation, especially when used as substantives. There is also the adjective mate in avoir la peau mate which is often used to describe a dark skin.

In general, referring to someone’s skin color might be touchy in France and other countries, as Sebastian Coltescu experienced a few month ago…