Some of the additional voters simply did not participate in 2004 and were sufficiently motivated in 2012. Also, Colorado continued to grow in voting age population, even during the Great Recession. And some of the increased vote was the much commented upon youth and minority voters, many of whom are a part of the large emerging Millennial Generation voting bloc. (cohort born from 1982 to 2000)
Millennials, born during or after 1986, were just 18 in the 2004 presidential election between George W. Bush and John Kerry. In 2012, an additional eight years of the generation joined the rolls, or about 70 percent of the estimated 80 million members.
National exit polls show they voted by 60 percent for Obama and, in general, are a more diverse and liberal generation.