"Race/ethnicity unknown" is the fastest-growing category reported for enrolled students in United States colleges and universities, with more than 1 million students so reported to the federal government in the most recent year.

http://www.acenet.edu/AM/Template.cfm?Section=Programs_and_S...

The federal regulations on the subject

http://www.ed.gov/legislation/FedRegister/other/2007-4/10190...

require all colleges to ask, but no students to tell, which of the federally defined race or ethnicity categories

http://www.whitehouse.gov/omb/fedreg_1997standards

they belong to. A growing number of students decline to answer the questions, which are clearly marked as optional on all college application forms. Harvard

http://members.ucan-network.org/harvard

reports 12 percent of its enrolled undergraduates as "race/ethnicity unknown," and several other selective colleges have higher percentages of students reported as unknown race or ethnicity. Several state university systems, by state law, may not consider student race or ethnicity at all as part of the admission process.

The definitive online FAQ on the issue of race and ethnicity self-identification in college admission in the United States

http://talk.collegeconfidential.com/college-admissions/12282...

links out to other relevant laws and official definitions and news stories, and gives links to reported enrollment figures for a wide variety of colleges.

After edit: A comment at the same comment level as this comment appears to be referring to a college's claimed rationale when it says:

I don't understand why they require ethnic proportions to stay close to population averages.

They don't. Indeed, it is strictly illegal to have admission quotas by race, since the Bakke decision decades ago. If you look at the actual enrollment figures, linked to from this comment, you will see that that is not what happens in practice either.

Another comment mentioned an applicant's view that he should not "lie about his race." This view motivates my children NOT marking anything on the forms, because the form questions are optional for applicants, and because my children think it is a lie to describe themselves as belonging to any narrower category than humankind. (From an old-fashioned American point of view, my children could be described as "biracial," but we prefer the term "human" and accept the term "postracial.")

I'm a baby boomer, which is another way of saying that I'm a good bit older than most people who post on Hacker News. I distinctly remember the day that President John F. Kennedy was assassinated--the most memorable day of early childhood for many people in my generation--and I remember the "long hot summer" and other events of the 1960s civil rights movement.

One early memory I have is of a second grade classmate (I still remember his name, which alas is just common enough that it is hard to Google him up) who moved back to Minnesota with his northern "white" parents after spending his early years in Alabama. He told me frightening stories about Ku Klux Klan violence to black people (the polite term in those days was "Negroes"), including killing babies, and I was very upset to hear about that kind of terrorism happening in the United States. He made me aware of a society in which people didn't all treat one another with decency and human compassion, unlike the only kind of society I was initially aware of from growing up where I did. So I followed subsequent news about the civil rights movement, including the activities of Martin Luther King, Jr. up to his assassination, with great interest.

It happens that I had a fifth-grade teacher, a typically pale, tall, and blonde Norwegian-American, who was a civil rights activist and who spent her summers in the south as a freedom rider. She used to tell our class about how she had to modify her car (by removing the dome light and adding a locking gas cap) so that Klan snipers couldn't shoot her as she opened her car door at night or put foreign substances into her gas tank. She has been a civil rights activist all her life, and when I Googled her a few years ago and regained acquaintance with her, I was not at all surprised to find that she is a member of the civil rights commission of the town where I grew up.

One day in fifth grade we had a guest speaker in our class, a young man who was then studying at St. Olaf College through the A Better Chance (ABC) affirmative action program. (To me, the term "affirmative action" still means active recruitment of underrepresented minority students, as it did in those days, and I have always thought that such programs are a very good idea, as some people have family connections to selective colleges, but many other people don't.) During that school year (1968-1969), there was a current controversy in the United States about whether the term "Negro" or "Afro-American" or "black" was most polite. So a girl in my class asked our visitor, "What do you want to be called, 'black' or 'Afro-American'?" His answer was, "I'd rather be called Henry." Henry's answer to my classmate's innocent question really got me thinking. Why can't individual human beings have the right to be treated as one more member of the general human race?