Even when a curb is not painted red you still cannot park your vehicle in front of any fire hydrant.
When you park your car you must park at least 15 feet away from any fire hydrant otherwise you'll get a ticket and possibly have your car towed away and impounded.
The red curb marking just allows drivers to notice a fire hydrant better but even when the curb is not painted red you still must park at least 15 feet away from fire hydrants.
Firefighters need access to fire hydrants in the event of a fire so you need to keep your vehicle away from the fire hydrant for safety.