From their Wikipedia page:
The 1962 Houston Colt .45s were an expansion team in American Major League Baseball’s National League, and 1962 was the first season in franchise history. Harry Craft was Houston’s first manager. The Colts finished eighth among the National League’s ten teams with a record of 64-96, 36½ games behind the league champion San Francisco Giants.
Check out this video when they wore the Colt 45 jerseys in 2012