GO GREEN AT COLORADO EARTH DAY CELEBRATIONS Saturday. Get a head start on Earth Day, Sunday, April 22, with a celebration only Colorado can throw. From 9 a.m. to 4 p.m. at the State Capitol, 200 E. Colfax Ave., celebrate the planet with yoga, live music and more. The family-friendly event will kick off with a good stretch and a little centering (that means yoga), an opening ceremony and featured speakers from athletes to politicians.