When you see a red a green and a white light on another boat?

When you see a red, green, and white light on another boat, it indicates that the vessel is underway and approaching you. The red light is on the port (left) side, the green light is on the starboard (right) side, and the white light is typically a stern light. This configuration helps you determine the boat's direction and position relative to yours, allowing you to assess whether you need to take action to avoid a collision.