Why are light-haired male love interests common? It is relatively common for series (especially shoujo) for the/a love interest to be blond. This appears in Ouran High School Host Club, Kaichou wa Maid-Sama, Tokyo Mew Mew, and a number of others. Why is this common in Japan, where the population is 98.5% ethnically Japanese--and as such naturally dark-haired--and most of the rest of the population is either Chinese or Korean?
It might have something to do with the representation of the blonde-color. According here, 


  Blonde hair on a male character may imply that he is a trickster.
  Alternately, it may symbolize that this character is a focus of chaos,
  and trouble follows him wherever he goes, such as Vash the Stampede
  from Trigun, or Soichiro Nagi from Tenjou Tenge; a live-action example
  is the movie version of Battle Royale's Kazuo Kiriyama. It is also not
  uncommon for anime males with long blonde hair to be portrayed as
  Casanova-types. (Examples: Kurz from Full Metal Panic, Allen Schezar
  from Vision of Escaflowne, Kyle from Suikoden V among others...)