Are ethnic "minorities" given preference in PhD admissions in the US? I have a question about college education, or more specifically, admittance into college education in the US.

Since as far as I remember, I've always heard that colleges or universities in the US have a sort of special preference for admitting people that are considered "minorities". I would like to know if this is true, and if so, what it entails. 

For example, I myself was born elsewhere but moved to the US at an early age, and eventually became a citizen. I don't know where this places me as far as "minority" programs go, if they exist. I imagine there'd be a sort of hierarchy such as scholarships > minority with scholarship > minority, but I really have no clue. 

This interests me because I am studying in a university outside the US, and I'm considering applying for a PhD program in the US. I'm aware that schools function differently, but if someone knows of this topic for a specific school it'd help.
There is a slight preference in the US for what are known as "underrepresented minorities"—that is, people who belong to groups who are not adequately represented in college enrollment relative to their proportion in the general population. That currently includes groups such as Hispanics, African-Americans, and Native Americans, but not groups such as Asian-Americans. So long as someone is a citizen, it does not really matter if one was naturalized or was a "born" citizen.

This does not mean that quotas are used, but it can be used as a "plus" quality in terms of admissions and hiring decisions.