In the last 30 years, the country has become steadily more racially diverse -- and so have many American colleges. In 1980, more than 80% of the country was white, and whites accounted for about eight in ten students at Harvard, Yale, and Princeton. Today, less than 65% of the country is white, and it's non-whites who now account for a majority at all three of those institutions.
The four graphs below compare national racial composition averages in 1980, 1990, 2000, and 2010 to six elite universities: three top-flight private schools in the northeast -- Harvard, Yale, and Princeton -- and three top-flight public schools across the country -- the University of Michigan, the University of Texas, and the University of California, Berkeley.* (University data comes from the National Center for Education Statistics. National data comes from the Census.) It is notable that the data below starts in 1980, two years after the Supreme Court ruled in Regents of the University of California vs. Baake that race could not exclude a candidate but could serve as one of many factors in college admissions.
There are any number of conclusions various people could draw from the data -- the under-representation of blacks is, of course, striking; some might say the flattening out of Asians at elite private schools suggests an unofficial quota system -- but I'll let the graphs speak for themselves. This post isn't meant to be a polemic, but rather a starting point, a primary source.