[1] Colby was selected to play in the U.S. National Team Development Program and represented the United States in the 2006 World U-17 Hockey Challenge, in a silver-medal performance.

[2] Committing to a collegiate career with Boston University for 2008, Cohen began the 2006–07 season with the USNTDP before leaving, citing unhappiness within his role, to join the Lincoln Stars of the United States Hockey League.

[7] Colby earned selection to the Frozen Four All-Tournament Team and was named the tournament's Most Outstanding Player after scoring the overtime game-winning goal, from a pass from defense partner Shattenkirk, in a 4–3 victory over the Miami Redhawks to win the 2009 National Championship.

[7][8][9] Returning for his junior campaign with the Terriers in 2009–10, Cohen was named as Player of the Month in January but was unable to help the team defend its National Championship after losing in the Hockey East Semi-finals.

[6] Upon signing with the Avalanche, Cohen moved directly into the American Hockey League and made his professional debut with the Lake Erie Monsters.

[13] After starting the season with the Monsters, Cohen was recalled by the injury-depleted Avalanche and made his NHL debut in a 5–0 shutout win against the Dallas Stars on November 6, 2010.