What color buoy indicates that you should increase your speed when entering the main channel?

The color that indicates you should increase your speed when entering the main channel is red. In the context of navigation, red buoys are associated with the starboard side of the channel when proceeding upstream (or returning from the sea). The Rule of Thumb for navigation states to keep red buoys on your right when traveling toward the head of a river or into a harbor. Entering the main channel typically means you are navigating in a more open area where it's expected that vessels can increase their speed safely.

The red buoy's presence signifies that the channel is well-defined and that you are moving toward a clearer, deeper water area, indicating it is appropriate to resume speed. This is crucial for efficient navigation and for adhering to maritime traffic rules, which aim to ensure safe and orderly movement in shared waterways.