Jeff is a wonderful man who wants nothing more than to make Fallon happy and provide for his children. He is the son of Jason Colby and Francesca Scott. Frankie was married to Jason's youngest brother Philip, but had an affair with Jason. When she gave birth to Jeff, Philip was fighting in the Vietnam War and was presumed dead. Frankie raised Jeff to believe that Philip was his father. When he was three-years-old, Frankie gave him to Cecil Colby and allowed Cecil to raise his nephew.
Living next door to the Carringtons, Jeff grew up with Fallon and Steven and from an early age loved Fallon. She never really gave him the time of day but he knew there was something special between them. He was thrilled when she asked him out on a date. Jeff had no idea that the date was set up by his Uncle Cecil. He also had no clue that his marriage had been a business transaction between Cecil and Fallon as a way to keep Cecil from calling in Blake's loan.
Jeff and Fallon tried to make their marriage work and when she said she wanted to try having a baby, he was ecstatic. What he didn't know was that Fallon only wanted to have a baby because Krystle was already pregnant. After Krystle's miscarriage, Jeff found out that Fallon was pregnant after he took a message from an abortion clinic confirming Fallon's appointment. He desperately tried to find out if there was any way to stop her from having the abortion, but was told that he basically had very few rights. Thinking that Fallon had killed their child, Jeff moved out of their bedroom and started divorce proceedings.
Drowning in his sorrows, Jeff was discouraged by Fallon's affair with Nick Toscanni and turned to Claudia for comfort. While he was sleeping with Claudia, Fallon gave birth to their son; Blake Jeffrey Carrington Colby prematurely. He later learns that Claudia was using him to spy for his Uncle Cecil. Cecil had blackmailed her by telling her that he would find Matthew and Lindsay in exchange for copies of Denver Carrington business transaction details. When he discovers what his uncle has done to him and to Claudia, Jeff tells Cecil that he never wants to see him again.
Jeff's world is turned completely upside down when his son is kidnapped. He is also faced with life and death when Cecil suffers a massive heart attack. While visiting his uncle in the hospital, he speaks of his son as if nothing was wrong and reconciles with Cecil. Jeff suddenly realizes that the cemetery caretaker took an unusual interest in the baby. Along with Blake, Jeff tracks down the caretaker and learns that he is the father of Alexis' former lover Roger Grimes, and more importantly, that Nick Toscanni arranged his child's kidnapping to avenge his brother's suicide.
When Cecil died, Jeff inherited half of Colbyco with Alexis getting the other half. Although he was working with Blake at Denver Carrington, Jeff moved over to Colbyco after Adam took it upon himself to make executive decisions without consulting anyone. Adam retaliated by having mercuric-oxide mixed with paint and used it to paint Jeff's office. Jeff was slowly poisoned and collapsed. On the rebound from Fallon, he impetuously runs away and marries Joseph's daughter Kirby. The marriage is doomed from the beginning because of Jeff's feelings for Fallon.
Kirby and Jeff divorced after she lost the baby she was carrying. The child was Adam's and she insisted that her marriage to Jeff was a mistake. Jeff was immediately jealous of Fallon's relationship with Peter DeVilbis and warned her not to marry him. He picked up the pieces of her broken heart and was pleased when Fallon accepted his second wedding proposal. Everything was going along quite well until Fallon suffered a debilitating headache and left on their wedding night, leaving Jeff desperate to find her. He was inconsolable when he thought Fallon had been killed in a plane crash with Peter DeVilbis.
Still in mourning but receiving tremendous pressure from everyone to move on with his life, Jeff became involved with Lady Ashley Mitchell. She was a bit resistant at first but Jeff swore he was in love with her and proposed shortly before they left for Amanda's wedding in Moldavia. He was heartbroken again when he found out that Ashley was one of the people killed in the massacre.
Jeff was beside himself and reluctantly agreed to help Blake with the pipeline deal with Jason Colby. Neither Jeff nor Jason had any idea that he is Jason's son. While he is in California, his Aunt Constance presents him with her half of the family business. Jeff is stunned that he is now a partner in Colby Enterprises. He returns to Denver to tell Blake that he and his son are moving to Los Angeles to keep an eye on Jason's business practices. He receives further incentive when Miles shows up at the Carrington mansion with Fallon. Jeff leaves for California that night.
When Miles arrives back at the Colby mansion in Los Angeles, he shocks the family when he introduces them to his new wife Randall. Jeff delivers the larger shock, Randall is his missing Fallon. Jeff tries to help Fallon regain her memory by telling her about the times they shared and their son Little Blake (now going by L.B.). She eventually regained her memory, had her marriage to Miles annulled and remarried Jeff.
Jeff helped Fallon through her second pregnancy and tried to keep her calm about the thought that the baby may not be his. He was thrilled when she delivered a little girl and tests proved that Lauren was indeed his child. By now Frankie had confessed that Jeff was Jason's son and the two men were trying to forge a relationship.
After Fallon was kidnapped by aliens and they returned to Denver, their marriage went downhill. Jeff had an affair with Ben's daughter Leslie. Fallon again filed for divorce and Jeff became involved with Sammy Jo. As with every other relationship they've had, Jeff and Fallon found their way back to each other.