a sail boat is heading straight at you
The same thing it does during the day.
Photosynthesis
It would help if you explained the context of it all, but I would imagine "light from above" means either the stars/moon in the sky, or with the guidance of God. I'm sure you understand what 'night' means.
A night during which you can not see the stars (because it is cloudy).
Good night
The same thing it does during the day.
a sail boat is heading straight at you
A green light is on the starboard side of the vessel. So it may mean that the starboard side is directly facing you.
a sailing vessel is approaching head on and you must give way
Navigation lights, green starboard and red port. Masthead and stern lights should be white
The Green Beans Green Warriors The Mean Greens The Mean Green Team
If you are operating a powerboat and see only a green light on another boat, that is a sailboat. The green light means you must give way.In a crossing or meeting situation it could mean you have the right away, however there needs to be more information to better answer the question. It does however mean that in some capacity you are observing the vessels starboard (right) running light.
Sailing vessel is approaching head on you must give away
Sailing vessel is approaching head on you must give away
Sailing vessel is approaching head on you must give away
fishing at night
Blue what ? ! ? Do you mean an object that appears blue in white light ? Such an object appears black in green light.