- Democratic congressional and state primaries: open
- Republican congressional and state primaries: open
- Democratic Presidential primary: open
- Republican Presidential primary: open
- As of 2016, Colorado has an open primary for presidential, federal, and state elections.
- 29% of registered voters in Colorado are unaffiliated or Independent.
Details of voting in congressional and state primary elections:
- Voters do not declare affiliation with a party in order to vote, but they must choose one party's ballot.
- minor parties may not allow unaffiliated voters to vote in their primaries.