Not only that, but "unaffiliated voters may affiliate at any time before and through the day of the primary election," according to the Colorado Secretary of State's office.
That gives unaffiliated voters in Denver a real choice: They could decide to affiliate with the Democratic Party by June 28, in order to have a voice on which of three Democratic candidates for Denver District Attorney make the November ballot: current state legislator as well as former deputy district attorney and Denver Manager of Safety Beth McCann; Kenneth Boyd, a senior Denver district attorney; or Michael Carrigan, former Denver deputy district attorney and University of Colorado regent.
But by instead affiliating with the Republican Party by June 28, an unaffiliated voter could help decide which of the five Republican candidates for U.S. Senate will take on incumbent Michael Bennet in November: Robert Blaha, Darryl Glenn, Jon Keyser, Jack Graham or Ryan Frazier, featured on our cover back in 2008 when he was an Aurora City Council rep. (For just a taste of their different styles, check out their campaign websites.)
Fair warning: You can only affiliate with one party for the primary — and you'll want to unaffiliate afterward if you want to avoid a lot of robocalls before election day. Need help deciding? Here's the list of all Colorado candidates who'll appear on a primary ballot.
Under the law established in 2013, you can register to vote up until the primary — but if you want a mail-in ballot, you'll have to affiliate by June 20. (You can do so at govotecolorado.com.) Otherwise, you'll have to go to an actual vote center and declare a party by June 28 in order to show your primary colors...