Republicans held only a 33-32 majority, and at least three GOP incumbents are trailing in their races.
If the trend continues, Mark Ferrandino of Denver is expected to become the first openly gay speaker of the Colorado House.
Only six months ago, an emotional Ferrandino watched as his bill to allow gay couples to form civil unions died in the Republican-controlled House after a night of unprecedented drama. Gay-rights activists at the time pledged to take out Speaker Frank McNulty and the GOP majority.
All 65 seats in the House were up for election, but there were few surprises in the majority of races, mostly because one party enjoys a clear voter registration advantage in that district.