The Black Knights have won three straight Patriot League regular-season games for the first time in four years and gave coach Zach Spiker his 50th career win at West Point.
Ellis, who came in averaging 16.4 points per game, was 11 of 15 from the field, hitting 4 of 7 3-pointers, and 8-of-10 shooting from the line.
Army (13-13, 6-5) avenged a 93-90 double-overtime loss to the Raiders on Jan. 23 and matched the program high for Patriot League wins in a season.
The Black Knights led by 15 in the first half. After Colgate closed to 49-45, Dylan Cox hit a 3-pointer, Jordan Springer converted a three-point play and Ellis hit a jumper to pull away.
Murphy Burnatowski’s 19 points led the Raiders (10-18, 4-7).