I have blonde hair! I recently learned that it's characterized by low levels of the dark pigment eumelanin!
What the heck is eumelanin?  I have never heard that term before!
It's a pigment! Specific blond hues depend on many things, but I guess it always results in some sort of yellowish color. 
Interesting!  Are blondes more common that brunettes or is about equal?
Brown hair is a bit more common, but there is a huge rivalry between blondes and brunettes! It's really a cultural phenomenon in many countries including the US, Canada and the UK! I think that's kind of silly!