How does sports betting work in Colorado? Christine Ricciardi, Boulder Daily Camera · February 26, 2020 at 3:52 am Slots, blackjack and video poker have been legal to play at casinos in a trio of Colorado mountain towns since 1991. But this spring, gamblers will have a variety of new ways to wager when sports betting becomes legal, too. Here are the basics of Colorado’s new sports gambling industry — and how you can double down on the action. Colorado voters legalized sports wagering in November 2019 with the passage of Proposition DD. It was a close call — the initiative passed with 50.8% of the vote.