I think Denver has "color-coded" their helmet shields, but the helmets themselves represent rank. Red shields represent a truck company and black for engines, but if the entire helmet is red, then it's probably an Officer of some kind.
Based on what I have seen, I believe that South Metro Captains and lower and Castle Rock Lieutenants and lower all have black helmets, but have different colored reflective tape on their helmets. Red reflective tape are for Captains and Lieutenants while yellow are for Firefighters. Any Chief (and Safety Officer in Castle Rock) have white helmets with yellow reflective tape,
Littleton has a similar set up except they have red helmets with yellow tape for Captains and red helmets with orange tape for Safety Officers. I don't know about their Lieutenants (unknown if the rank exists).