Colby Granger (portrayed by Dylan Bruno) is a FBI agent on the American television show Numb3rs. First introduced during the second season, he has become a part of the team led by FBI Special Agent Don Eppes (Rob Morrow) and is usually partnered with David Sinclair. This connection creates some tension when Colby is accused of being a spy for the Chinese.

Colby is introduced in the second season as a rookie Federal Bureau of Investigation agent. David Sinclair is his usual partner. Granger idolizes the legendary sniper/tracker Agent Ian Edgerton. Granger had recently begun carrying the .45 ACP caliber Springfield Armory Custom TRP (Tactical Response Pistol) Professional Model, which indicates he is SWAT/HRT qualified, as only SWAT/HRT qualified FBI agents are authorized to carry that weapon on duty. As new partners in season 2, David and Colby seemed to disagree with each other on methods used while working on cases. For the first few episodes, they did not seem to like each other at all.

Over time, however, they became very close friends.
At the end of Season 3, it was revealed that Colby Granger had been spying for two years for the Chinese, as had his "old Army buddy" Dwayne Carter (Shawn Hatosy), who he covered for and then sent to prison in "The Mole". His fellow FBI team was shocked, with his partner Sinclair taking the betrayal especially hard. Colby was immediately removed from the team and incarcerated. However, in the Season 4 premiere he escaped while being transported to another prison and it is revealed that he was actually only acting as a triple agent in order to help out the U.S. counterintelligence.

This could not be confirmed because his supervisor and sole CI contact, Michael Kirkland, had been killed. Any doubt of his status was finally removed when the agents rescued Colby from being killed by Chinese spies on a ship heading for international waters. Dwayne Carter dies, saving Granger once more by taking out torture expert Mason Lancer (Val Kilmer). Colby was offered a job in Washington, D.C., but chose to stay with his former team. David was distant with Granger, which caused their team to perform poorly on a mission, and caused Don to reprimand them. Afterwards, the two reconciled and Granger was welcomed to stay with the team.

Among the team, Colby's experiences as a triple agent have been referenced several times, and, once, Colby cites it as a reason for not dating. When FBI Special Agent Roger Bloom (Henry Winkler), a 34-year veteran of the FBI's bank robbery division who lost his job because he stole 10 million dollars (US) to draw attention to a 2,000 dollar (US) theft at his sister's store, tries to solve a series of unsolved bank robberies, Colby relates his own experiences to Bloom. Moreover, when FBI Special Agent Ian Edgerton (Lou Diamond Phillips) takes Colby hostage after being arrested on murder charges, Ian references Colby's experiences in an effort to earn Colby's sympathy. Colby, however, insists that his experiences and his current circumstances are different. Only when David uses his and Colby's distress word to alert Colby to impending danger does Colby realize that Ian is innocent of the charges. Colby did a tour of duty with the U.S. Army's Criminal Investigation Division in Afghanistan before joining the FBI, wherein his friend Dwayne Carter saved him from a car explosion, making him indebted to Carter in Dwayne's eyes. After getting his college degree, Granger received three years of training in interrogation techniques.

He was raised in Winchester, Idaho and plays golf in his spare time. He is also fluent in Spanish and was a wrestler in high school. His father died when he was 15. He apparently enjoys fishing. He spent some time in Oahu where he enjoyed surfing as was seen in the episode, "Charlie Don't Surf".