And if they do? They can vote in that party's primary -- and potentially change the game.
"This is a law that was passed by the legislature, signed by the governor. So it's not a partisan issue -- you can affiliate either Republican or Democrat," says Ellen Dumm, executive director of Campaign for a Strong Colorado, which represents a coalition of political groups. "It's just a matter of what race you are interested in."
And with the mud still wet from the recent slinging in the increasingly down-and-dirty Democratic Michael Bennet versus Andrew Romanoff Democratic Senate contest, the Jane Norton versus Ken Buck Republican Senate contest, and the Scott McInnis versus Dan Maes Republican gubernatorial race, what isn't interesting?
The only problem is, if you're unaffiliated, you can only affiliate with one party today -- and to find out how to do so, contact your county election office, or try the Secretary of State. And remember -- tomorrow, you can unaffiliate again.
Depending on how today's vote goes, you may want to.
For the record, as of July 1, here's how Colorado's voter registration broke down: 765,849 unaffiliated; 817,458 Democrat and 855,667 Republican.