Green lights slowly moving and alternating in color from green to white to green again

While on a sailing vacation in Tonga (Va'vau) we were anchored and cooking dinner at approximately 9 or 10 pm (I beleive it was in May 1992).  
I noticed 2 green lights approximatly 1/2 mile away and 10 - 20 feet above the surface of the water.  No sound. I thought they could be some kind of vessel's navigation lights but there would be no vessels out there due to the known hazard of navigating where we were at night.  They appeared to be moving slowly back and forth past each other and alternating from green to white every few minutes.  
This made me think they were not navigation lights since they would be green and red if they were (not green and white).  Also, navigation lights do not alternate color.  
I was able to take quite extensive video of this event which went on for 1/2 hour or more.  
They eventually moved off and disappeared behind an island. 
I am searching for this video in my storage and would like for someone to look at it and give me their opinion.
Witness indicates that the date of the incident is approximate.  PD