Lawmakers in Colorado and at least five other states are considering changing that, proposing bills to roll back legal protections for gun manufacturers and dealers that have kept the industry at arm’s length from questions of blame. A draft version of Colorado’s bill, expected to be introduced Thursday, not only repeals the state’s 2000 law — which broadly keeps firearm companies from being held liable for violence perpetrated with their products — but also outlines a code of conduct that, in part, targets how companies design and market firearms. If Colorado’s bill passes, the state would join California, New York, Delaware and New Jersey, which have passed similar legislation in the last three years.