Becoming brown I assume, without more context, is to indicate white as decreasing in overall percentage of racial makeup of the US.
The non-Hispanic White percentage (63% in 2012) tends to decrease every year, and this sub-group is expected to become a plurality of the overall U.S. population after the year 2043. White Americans overall (non-Hispanic Whites together with White Hispanics) are projected to continue as the majority, at 73.1% (or 303 million out of 420 million) in 2050, from the current, official 80%.
Plurality means there are more of one group than any another, but this doesn't mean more than all the other groups combined; that's a majority.
met with shrugs means "So what?". This is a change from displaying a firm bias for/against a certain position. In this case, "acknowledgement of sexual identity." Or, in other words, if a student claims to be homosexual, lesbian, etc., this claim is increasingly met with a lack of reaction.