AG99: Not all voters received ballots, as this article explains. As of November 1, 2017, however, the Colorado Secretary of State reported there were 1,720,236 active, registered female voters; 1,607,825 male voters; and, 46,738 "gender unknown" voters. An additional 35,469 voters were preregistered, divided almost evenly between genders. 

 http://www.sos.state.co.us/pubs/elections/VoterRegNumbers/VoterRegNumbers.html