https://www.theguardian.com/us-news/...-car-ban-sales
California has banned sales of new gasoline powered cars starting 2035. Washington and Massachusetts have followed suit.
I am certain Colorado will follow that lead, the only question is how soon.
If the legislature continues being Democrat controlled, my guess is during the next session.
Place your bets.
Edit to add- In 2018 Colorado passed a law requiring the state to follow California emission laws.