Final answer:
A blue flag used by utility operators to mark underground utilities signifies potable water services, following a standardized color-coding system.
Step-by-step explanation:
When a utility operator locates underground utilities and marks the location with a blue flag, the color represents potable water services.
The standardized color-coding system for locating and marking underground utilities is essential for safety and efficiency, ensuring that excavators and the public are aware of the type of utility in a specific area.
This system helps prevent accidental damage, service disruptions, and potentially dangerous situations.