According to COLREGS "(b) A vessel of less than 50 meters in length (at anchor) may exhibit an all-round white light where it can best be seen instead of the lights prescribed in paragraph (a) of this Rule."
i have seen the ineffectiveness of masthead lights personally.
i use a very bright led in a perko lantern into which i have installed led BRIGHT white light. the original was only visible for 3 miles.. now it has 5 mile visibility, placed in the foretriangle is visible to all, pangas and sailboats and powerboats.
i have witnessed how masthead lights blend in with the ambient hillside local house lighting and made mine better and more visible.