If you see a red light on another boat?

If you see a read light on a boat, then you are seeing it's port (left) navigation light. These lights indicate the that boat is moving, and which way. Since you are seeing the left, it is moving from right to left. Much like in a car, the driver on the right has the right of way. I remember this by red = stop (other driver has right of way) - green = go (you have right of way) - this is pretty obvious. As far as colors - Red is NOT Right (even though they both start with R), that's how I remember it. As far as Port/Starboard, I remember with this song http://www.nightheron.com/trees_activityguidebarges.html - my mom used to sing that line to teach me the colors.

Red and Green means the boat is coming toward you, and White means the boat is under power (if seen at the same time as the red or green) - or anchored/moving away from you if seen by itself.