People will generally tend to select their partners based on a series of factors, based on appearance, personality, interests, etc. These factors will tend to cross and mix the more parters the person has.
In general if you notice that x ammount of partners posess x characteristics, then yeah, you probably have a 'type' - and you'll tend to prefer people who match closely to that 'type'.
This doesn't mean that there aren't exceptions - like, say, the majority of the people you dated were blonde. Doesn't mean you dislike brunettes. You could date a brunette or a redhead, provided they connected with you in another way.
But for the most part, you prefer blondes, Because your past expoeriences have given you an idea of what to expect with blondes, and most of the ones you meet/date fit the mental image you have of them.
TL

R - Yes, everyone has a type. Eberyone ahs several types. You just need to sort out which factors are important to you.
... man i think i wondered off topic. Should really stop using internet when drunk