The green light is on the vessel’s starboard side, and the red light is on the vessel’s port side. The white light is on the stern, or back, of the vessel.
So if you are putting a red and green combination light on your boat, you must ensure that it meets USCG standards and shows the correct field of view.
Combination lights on the bow are common on smaller boats. They make both red and green lights with a single bulb and have the appropriate viewing angles.
And finally, a white stern light pointed aft. A Sailing vessel under sail does not need the forward masthead light, but they need to turn it on when under power.