Rules of the Road
Lights & Shapes, Rule 21-International
Definitions
(a) "Masthead light" means a white light placed over the fore and aft centerline of the vessel showing an unbroken light over an arc of the horizon of 225 degrees and so fixed as to show the light from the right ahead to 22.5 degrees abaft the beam on either side of the vessel.
The masthead light is typically white in color. It is displayed at the top of a vessel to indicate the presence of another vessel at night.
The arc of visibility for a masthead light is 225 degrees. This means that the light must be visible from dead ahead to 22.5 degrees abaft the beam on either side of the vessel.
A masthead light is a white light located at the highest point of a vessel, typically on the mast or superstructure. It helps other vessels identify the boat's presence, direction of travel, and size when navigating in low visibility conditions. The masthead light is required by maritime regulations, especially at night or in restricted visibility.
Rule 21 of the Navigational Rules of the Road. (a) "Masthead light" Means a white light placed over the fore and aft center-line of the vessel showing an unbroken light over an arc of the horizon of 225 degrees and so fixed to show the light from right ahead to 22.5 degrees abaft of the beam on either side of the vessel, except that on a vessel of less than 12 meters (39'4") in length the masthead light shall be placed as nearly as practical to the fore and aft center-line of the vessel.
Generally they are masthead light, port and starboard steaming light and stern light. Others may be displayed depending on the length of the vessel and what duties it is carrying out.
The green light would be the starboard steaming light, the white the masthead light. What you would do would depend on factors such as its releative bearing and in what waters you are sailing.
Navigation lights, green starboard and red port. Masthead and stern lights should be white
Without seeing the actual configuration there isn't enough information to make a decision. Am I seeing the port side aspect of of the vessel? A port side running light at 112.5 degrees and a masthead light at 225 degrees? Where are the lights in relation to each other?
Yes, it is.
A white masthead light must be shown when a powerboat is operating at night.
The characteristics of navigation lights on a power driven vessel includes sidelights, sternlight, masthead light, and all-round white lights. Navigation lights must be displayed from sunset until sunrise as well as anytime visibility is restricted.
The masthead light should be visible in a 225 degree arc centered on dead ahead.