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!
That is funny!  Why on earth would there be a rivalry over different color hair?
Blond
Blond or fair hair is a hair color characterized by low levels of the dark pigment eumelanin. The resultant visible hue depends on various factors, but always has some yellowish color. The color can be from the very pale blond (caused by a patchy, scarce distribution of pigment) to reddish "strawberry" blond or golden-brownish ("sandy") blond colors (the latter with more eumelanin). Because hair color tends to darken with age, natural blond hair is generally rare in adulthood. Naturally
after black. It is caused by higher levels of the natural dark pigment eumelanin, and lower levels of the pale pigment pheomelanin. Brown eumelanin is more common among Europeans, while black eumelanin is more often found in the hair on non-Europeans. A small amount of black eumelanin, in the absence of other pigments, results in grey hair. A small amount of brown eumelanin in the absence of other pigments results in blond hair.
In Western popular culture, a common stereotype is that brunettes are stable, serious