Are you talking about different types, or different colors? In my department (volunteer department) we all wear the traditional style once you have established that you are going to stay with the department for a little while...until that point you are issued a "salad bowl" or modern style helmet. There are many types of helmets out there, traditional, modern, rescue, wildland, ect.
As for colors, it will vary by department. My department is:
Chief and Captain, White; Lieutenant, red; everyone else, yellow; cadet (youth program), black
The department next to us has White for chief, assistant chief, captain; yellow for lieutenant; blue for firefighter
Chief (any rank of Chief) White
Capt, Lt, Paramedic officer, Driver, FF/PM, FF, Cadet or Interns are Black. Rank is differentiated by the front piece they have.
Some of our civilian staff have Yellow if they have a reason to be on a scene such as PIO or part of the ICS staff.
Cadets and Interns have different gear than the rest so they can be quickly ID'ed on the fire ground.
There really is no standard regarding helmet color, there are general guidelines but no real 'rules' dictating what color a fire helmet should be. This is left up to the individual departments where anything goes...
Typically, firefighters and engineers wear black or yellow helmets. Black helmets are considered old school by many...
I think most people associate firefighters with yellow helmets, and the kids love them too!
Fire Captains, and again this is a generalization where red fire helmets... which used to look like this back in the day...
Now, all helmets must pass safety standards to ensure maximum protection from blunt trauma or other materials that could cause injury or death. Typical Fire Captain helmets look like this: