The red and green lights are sidelights that are positioned on the port side (red) (left as facing the bow) and starboard (green) (right as facing the bow) side of the boat. Various white lights are required depending on the size of the boat, but generally, a white masthead light and stern light are required. See the US Coast Guard site in the link below for more specific information.
If you see red and green (with the red on the right and the green on the left), it's a vessel heading directly towards you (although its course may be different). The white (single) light would indicate that it is a powered vessel as opposed to a sailing vessel.
If you observe just the red light on a ship, they have the right-of-way and you are to maneuver to stay clear. In this case, both vessels should take precautions. In any case, the default maneuver is to turn starboard (to the right).
Advisory:
Please read the discussion to this question.
When you see a red, a green, and a white light, you are approaching another power-driven vessel head-on and both vessels must give way.
a boat is approaching you head on
dark out
dark out
dark out
dark out
dark out
Its a motor boat, coming straight against you.
you are approaching head on.
it tells you the boat is approaching you head on
If you see both the red and green lights but not the white one, the boat is coming right for you and something's wrong because the white light has to be visible from any angle for a distance of two miles. <<>> If there's no white light it's a sailing boat. If you see red and green the boat is under sail and you are lined up with its bows. A small motor boat also needs a white light high up and visible all round.
If you see both the red and green lights but not the white one, the boat is coming right for you and something's wrong because the white light has to be visible from any angle for a distance of two miles. <<>> If there's no white light it's a sailing boat. If you see red and green the boat is under sail and you are lined up with its bows. A small motor boat also needs a white light high up and visible all round.
When you see green and white lights on another boat, you should slow down. This means that you are approaching another boat and you should reduce your speed.
If you see both the red and green lights but not the white one, the boat is coming right for you and something's wrong because the white light has to be visible from any angle for a distance of two miles. <<>> If there's no white light it's a sailing boat. If you see red and green the boat is under sail and you are lined up with its bows. A small motor boat also needs a white light high up and visible all round.