Just behind him at minus-11 are Joe Inman (65) and defending champion and playing partner Bruce Fleisher (67). Rocky Thompson (67) and Mike Hill (66) are three back at 9-under.
Coming off a bogey-free round of 64 on Friday, Colbert was still blemish-free through 15 holes on Day 2. The 59-year-old veteran had already recorded five birdies on the day, but a lone bogey at the par-5 16th cost him a bit of space.
As a result, and because of late birdies from Fleisher at the 16th and 18th holes, Colberts lead ' which during the majority of the day was three shots ' was cut to one.
Yet, he is still in good shape for his second win of the year.
Colbert claimed victory earlier in 2001 at the SBC Senior Classic. The win was his first since 1998, when he edged out Jose Maria Canizares by a shot. He then went on to win the unofficial Liberty Mutual Legends of Golf with Andy North.
Should he hold on Sunday, however, he will, in all likeliness, have to hold off Fleisher. The two-time defending champion is looking to become the first-ever player to win this event three times in a row.
Full-field scores from the Home Depot Invitational