That pattern held in 2014, according to data just released from the Census Bureau -- except, to a small extent, that last bit.
In 2014, the percentage of voters that wasn't white was at the same level as in 2008, 23.7 percent. That's pretty staggering: 2008, then high-water mark of a diverse electorate is now the norm in off-year elections.
Part of the change is because of demographics. Older voters continue to be vastly overrepresented on Election Day, in part because they tend to check a lot of the boxes we presented at the outset.
As a result, relative to their density in the population at large, people over the age of 65 voted 8.3 percentage points more heavily. People under 35 voted 13.2 percent less than their representation in the population might suggest. (Well under one-in-three people under the age of 35 reported voting in 2014.)
That older vote is likely why the Republican party did so well last year. But the other demographic shift is that America itself is getting less white. Relative to their representation in the population at large, black Americans turned out more heavily in 2010 and 2014. But Hispanics turned out less heavily. (For the sake of ease, the terms "white" and "black" in this article mean white and black non-Hispanics.) That may in part be due to the fact that the Hispanic population skews younger than the rest of the country.
The shift is not only due to demographic changes, though. "[T]he question of whether these changes in the electorate are being driven by simple population change, or by increased or decreased engagement from certain groups," the Bureau's Thom File writes, "remains an open question." The "increased engagement ... from certain groups" certainly could include a black voter base that's been energized since the election of Barack Obama; note the changes in 2010 and 2014. But black voters are also the one group that has voted in off-year elections steadily since 1978. White and Hispanic voters now turn out far less.
The electorate is slowly shifting to look like the future population: more gray and less white. It also continues to trail the population significantly in how closely it matches that population.
Over the short-term, it probably doesn't mean much for politics: 2014's electorate was less white than 2006's, but the results in the House were very, very different.