There are probably no Grizzly bears in Colorado, although it's possible in the far north I suspect.
Black bears are curious animals, rarely agressive towards people, but can be pests if allowed to eat human food even once. I'd be especially cautious if a bear returns to your campsite repeatedly after being chased off or isn't easily chased off - I'd move to a new campsite if that happens.
I've never carried mace, but it's not a terrible idea if you find a product with good evidence for effectiveness.
Also, if you follow standard bear country precautions, any unnatural encounters will be very rare. Cook and eat away from where you sleep. Hang food and any other scented items in a tree away from where you sleep. Keep a clean camp. And don't use soap or deodorant before going to bed.
It's really the bears that are in danger, not people. "A Fed Bear is a Dead Bear." Once bears are no longer afraid of people or associate food with people, they have to be destroyed. Unfortunately it's sloppy car campers, RVers, and local homeowners that create the problems, putting both backpackers and bears in danger.
As far as wearing bells while hiking, that's completely unnecessary in black bear country, and rather silly. If you're hiking along and come across a bear, they'll be busy doing natural bear things, and the encounter will be a rare treat. Do you blow air horns while hiking in Illinois to avoid seeing deer or turkeys? If you don't want to see wildlife while visiting the wilderness, perhaps a trip to the theatre or city park would be more to your liking.
-Bob