I was born and raised in New Haven, CT. The firetrucks were and are WHITE. We owned a business in Hamden, CT the trucks used to be a Yellowish Green Color. Now they are Red with white upper sections.
The town I live in now uses red trucks.
40 years ago I was in business in Danbury. Paid firefighter drove red trucks, the volunteer companies drove the color of their choice.
It is up to the individual municipality to decide.