Answer: In order to determine which boat is a give-way vessel and which boat is a stand-on vessel, one must look at the direction from which the other vessel is approaching.
If a vessel appears to come from the right side, then that vessel is the stand-on vessel and the other is the give-way vessel. Therefore, the give-way vessel must take instant action to avoid the crash.
At night, the lights are used for communication purpose, of which the green light depicts the starboard side and the red light depicts the port side.