Who is white? What are the criteria? Is it the paleness of one's skin? If that were the case then Takao Ozawa (1922) would have been granted naturalization, since his skin was white. But he was Japanese, so the Supreme Court determined that white meant Caucasian.
So a white person is someone who is Caucasian? Well... not exactly. When an immigrant from India, Bhagat Singh Thind (1923), attempted to gain citizenship by arguing that he was Caucasian. He was rejected, using a weird non-definition of white, appealing to the authority of the common man, whoever he is: "the average man knows perfectly well that there are unmistakable and profound differences" between a South Asian and a white person.
As any sociologist will tell you, race is meaningful only as a social construction. There's no significant difference between "races", except for their shared experiences (i.e. ethnicity or cultural differences of course, but mostly the shared experience of being discriminated against, being designated "other"). Whiteness in America was constructed as a legal system designed to economically benefit a small elite, by entrenching disadvantages for most groups.
It was also designed to "divide & conquer", to prevent the feared solidarity between white indentured servants and black slaves. (see People's History of the United States)
There's no essential "white". Neither is there a monolithic group of "non-whites". The connecting thread among so many diverse groups is that experience of being excluded from certain things that white people take for granted - being marginalized.
For a really interesting discussion about the complexities of marginalization, read Intersectional Identity by Thinking Girl.
Today is International Day for the Elimination of Racial Discrimination. Check out this research project: Discrimination in the Job Market: Are Emily and Greg More Employable than Lakisha and Jamal?
Also read the 10th Erase Racism carnival.