The Steelers used the franchise tag on Bell last spring, who subsequently played the 2017 season with a $12.1 million cap hit.
"I don't like to get into too much detail," Colbert told reporters Wednesday. "I can say this, though: I'm optimistic that we can find common ground. Those things are never final until they're final."
Colbert appeared reticent to use the tag on Bell for a second consecutive year, but didn't rule it out as an option. If both parties can't agree upon a contract by March 6, Bell is scheduled to become a free agent on March 14.
"We'll never say the tag is not available because it's a collectively bargained item that, if need be, will be put into use."
Bell is establishing himself as arguably the NFL's best running back, earning his second first-team All-Pro selection in 2017. The 26-year-old rushed for 1,291 yards and nine touchdowns, adding 86 receptions for 655 yards and two touchdowns.
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