NFA items, including silencers, are illegal in Colorado by state law.
It is an "affirmative defense" if "said person has a valid permit and license for possession of such weapon." Having your NFA Form 4 or 1 or other Form in the registry is considered having a permit or license.
If the registry is eliminated it takes away the affirmative defense. No more NFA in Colorado.
It looks like the RIFLE Act would keep the Forms and Registry so Colorado citizens would still be able to legally own NFA stuff.