BOULDER — Colorado coach Mel Tucker, at a practice earlier this week, said it was a beautiful day for Buffs football because all he sees is “green grass and opportunity.” While he wasn’t directly referring to his green group of running backs, it was apropos for a young unit featuring four underclassmen. At the top of that list may very well be true freshman Jaren Mangham — the highest-rated recruit of the bunch, who turned heads with a breakout spring game. A four-star recruit out of Detroit’s Cass Tech, the 6-foot-2, 215-pound Texas native chose CU over dozens of offers, including from the likes of Michigan State and Texas A&M. “It was pretty hard,” Mangham said of his recruitment, “but I wanted to experience something new.” That experience could come right away. Mangham is competing for the starting spot with sophomore Alex Fontenot and redshirt freshmen Jarek Broussard and Deion Smith.