The legal action comes as the Colorado GOP is set to gather Saturday to consider a bylaws amendment that would make it easier for Republicans to opt out of state primaries next year altogether
Even in new York only people registered under a specific party can vote in that party's primary. So only Dems can vote in the democratic primary. If you're registered for any other party, or registered as unaffiliated you cannot vote in the democratic primary.
I disagree with this set up but the GOP in Colorado aren't really doing anything radical with this.