Hola Alex

We say that someone "tiene el pelo claro" to refer to "hair of a light colour, e.g. blond, very light brown...) as opposed to "tiene el pelo oscuro" that refers to black, brown hair. 

As a more direct translation of "being blond" we would then say "Es rubio/-a".

I hope this clarified it and you enjoyed the Mafalda reader. 

Un saludo

Inma