|Betty and Veronica|
A classic example of blonde versus brunette
To understand this theory you have to appreciate the different qualities of dark and light, black and white, night and day. You see, symbolically black represents darkness and in darkness not everything can be known because the darkness hides some things. On the other hand white represents light and with light everything is revealed. So, subconsciously a brunette is seen as mysterious because subconsciously the darkness of her hair represents that which is not know.
A brunette is often full of surprises since you can't know everything about her. She is often more serious and studious than her light haired counterpart, seeming to weigh and consider all information before making a decision and in turn she is taken more seriously by others. To illustrate this I did a Google image search for "mysterious woman" and of the first 20 images of women all but three were brunette.
Meanwhile the blonde is seen as an 'open book' because her hair represents that which is revealed because of the light. The blonde has no secrets, she has a light and airy persona, meaning a personality that is more bubbly and vivacious. She is more likely to make snap decisions and deal with the results or consequences later.
I truly believe the subliminal perception we have of brunettes and blondes is the basis for the stereotypes we have today of these women, especially blondes. I'm sure you're thinking "what about blondes who are naturally brunettes." Well I feel my theory still holds up because a brunette who goes blonde tends to take on more of the persona and traits I've attributed to that hair color. The same goes for blondes who turn brunette.
I've often said "brunette's are the ones you take home to meet your parents, the ones you build a life with, blondes are the ones you have fun with, the ones you enjoy life with." Neither one is better or worse than the other, they both have their merits, their value, their desirability.
And then there's the redheads... :)