That's a very valid assumption. Apparently, there must be a gigantic reflection that makes the Moon look green-ish! If it was Blue, that would make sense since the Ocean is always blue-ish!
If you compare this image to the image of VII, you can sense some strong similarity!
The logo of Final Fantasy VII has a White Materia on it and it has green-ish colour
And why 7 ships? Why can't it be 6 or 8 ships?
There you go!