John Mosley came to the Colorado A&M Aggies in 1939 as a National Merit Scholarship student and decided to play football for football coach Harry W. Hughes. When Mosley stepped onto the football field he became the first black college football player in the Mountain States Conference (Skyline Conference) and first in the state of Colorado in over 30 years. Mosley played various positions on the varsity team of the Colorado Aggies between 1940 and 1942, including fullback. John Mosley battled discrimination from other football teams, and with the help of his teammate Lewis "Dude" Dent he was able to break color barriers in sports throughout the Rocky Mountain Region.
John Mosley wrestled for Aggie wrestling coach Julius Wagner at Colorado State during his college days. Mosley won all-conference honors as a wrestler and in his junior and senior years, Mosley was elected to be the class vice president.
In 1998, John Mosley was elected to the Colorado State University Sports Hall of Fame for his achievements in football and wrestling. In 2009, Mosley was inducted into the Colorado Sports Hall of Fame as a great athlete and pioneer of Colorado sports.