It widely varies around the country. Some, are confusing with the multiple color helmets and turnout gear.
In NYC, Firefighters and Company Officers have black helmets. The Firefighters have an insert in the frontpiece indicating the Company number, the background color of the insert denotes the type of Company i.e black-Engine, red-Ladder, blue-Rescue, green-Marine, yellow?-Squad. At the bottom of the frontpiece is their badge number.
The Company Officer has a white frontpiece with the Company number and the background color denotes the type, same colors as stated above. The bottom of the frontpiece will have either Captain or Lieutenant.
Chief Officers wear white helmets with a gold frontpiece that shows Battalion number, Deputy Chief, Deputy Asst. Chief and so on.
There's also some special helmet frontpiece setups out there for Field Comm, Chiefs Aides etc.
Down here in Va. Beach Firefighters wear yellow helmets, Capts. & Chiefs wear white helmets