Under what condition may a train increase speed after encountering a color light signal displaying an aspect of restricting?

The correct choice indicates that a train may increase speed after the entire train has passed a more favorable signal. This aligns with standard operating procedures regarding signal aspects. The aspect of restricting generally means that the train must proceed at a reduced speed for safety reasons, typically due to track conditions or other operational limitations.

Once the entire train has passed a more favorable signal, which indicates a higher permitted speed, the train crew can then safely accelerate, as the restrictive condition is no longer in effect. This ensures that all parts of the train are clear of any potential hazards that may have necessitated the initially restricted speed.

Other conditions listed do not provide a basis for safely increasing speed. For example, departing from the station does not imply that the restrictive condition has been lifted. Authorization from the dispatcher does not generally pertain to signal aspects; signal indications govern speed limits. Lastly, waiting for a signal from the conductor lacks the regulatory backing that passing a signal provides for speed increment. Thus, the most appropriate answer is based on the operational guideline that emphasizes the importance of signal indications for safe train operations.