Colman has competed at four IPC Athletics World Championships. In 2002, he won a bronze medal in the Men's 400 m T53. In 2006, he won a bronze medal in the Men's 800 m T53. At the 2011 Championships, he won a gold medal in the Men's s 800m T53 and a silver medal in the Men's 400 m T53. At the 2013 Championships in Lyon, France, he won bronze medals in the Men's 800m and 1500m T53 events. He was selected to compete at the 2015 Championships in Doha but withdrew from the competition.