What is it about the combination of blonds and brunettes?

[readbeforesleep]

My history of OTPs

2000 - Spike/Angel
2001 - Spike/Xander
2003 - Draco/Harry
2009 - Arthur/Merlin
2010 - John/Sherlock
2011 - Esca/Marcus
2011 - Brad/Ray from Generation Kill

And the thing is, I never liked blond guys in my youth. Now, it's the hair color I prefer.